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SNOWMOBILES - Vintage Snow

1. iE SNO TWISTER HI PERFORMANCE NO 74 1 Flash Inside Info for Mercury Snowmobile Dealers to Z i p to INTRODUCTION Their Sno Twister Customers 11 16 73 It s official After months of spinning on hay and straw or on just plain grass the snowmobile season on good old Alaskan snow has opened with a resounding Margin for Mercury Eager sponsor of the kick off race meeting on Nov 3rd and 4th was Brandt s Lodge and if you re real quick in geography you ll find it 160 miles northeast of Anchorage Give or take a couple of months that can be real mean blizzard territory Ignoring all impending hazards however were local drivers who had WIN written all over their Sno Twisters The Sno Twisters leaped to the front and stayed there to win all three heats in their 400 class plus the final around the oval all on Saturday Then Sunday the crew came right back to grab first place honors in cross country 50 here s the bonus We of course are happy to share the secrets of success so that you too can make the run for the roses The following procedures were used in setting up the champion Sno Twisters at Brandt s Lodge ENGINE 1 Check timing 83000 RPM 100 005 BTDC 2 Adjust idie slow enough to allow clutch to reset Too high idle speed will cause partial engagement and belt drag resulting in a slower start off the line 3 Check for proper jetting The following jet sizes will serve as
2. advise Mercury Marine Publications Dept P O Box 1108 Fond du No 15 8 12 6 4 Lac WI 54935 and give the first number that you received TRACK STUD INSTALLATION 1975 Models 340 S T 440 S T and 440 T T Chassis Serial No 4205000 and Above On some snowmobiles wear strips D 70727 in the chassis tunnel will require repositioning if installation of track studs is desired Make certain that the FRONT END of both wear strips extend 4 10 16cm forward of FRONT wear strip attaching hole in chassis Failure to observe this dimension exactly may result in damage to the chassis tunnel with track studs installed If wear strips are not correctly positioned reposition as follows 1 2 3 e Remove seat cushion fuel tank and slide suspension Drill out 14 rivets which attach wear strips to chassis and remove wear strips Reposition each wear strip so that the front end extends 4 forward of front wear strip attaching hole in chassis Using wear strip as a guide drill 13 64 5 16mm holes thru chassis 7 for each wear strip Install fuel tank and seat cushion Attach wear strips with 14 rivets C 17 7 1790 Install slide suspension and readjust track tension and alignment P 90 0 bu ji i 2 NOTICE Sno Twister Hi Bedonnance Tipsters are in numerical order starting with 75 1 If the first copy you receive is example 75 3 and you desire previous Tipst
3. 14 7mm SKI ASSEMBLIES T Check both leaf springs to make certain that they move freely in the plastic slides If necessary grind or file the sides of the spring as required 2 Check the curl of the leaf spring top forward end to make sure that the curl does not hit the shock absorber when the spring is collapsed if necessary grind or file end of spring curl as required CARBIDE SKEGS Starting with Standard Carbide Skegs D 74783 1 ten 1 carbide segments numbered 1 thru 10 tront to rear 1 Move carbide segment Nos 1 and No 2 behind No 3 Move No 4 carbide segment behind No 10 2 Depending upon conditions and individual preference you also may want to add two more 1 carbide segments one behind No 3 and one behind No 10 4 and 8 10cm and 20cm carbide skeg SUSPENSION ADJUSTMENTS Initial suspension settings should be T Front arm in upper chassis hole and middle hole on the suspension 2 Set the springs quite stiff Weight transfer effect can be increased by increasing the angle of the front arm lower hole in the suspension Weight transfer effect can be decreased by decreasing the angle of the front arm lower hole in chassis or upper hole in suspension E E NOTE Less weight transfer effect results in more ski pressure while accelerating TRACK Handling on hard ice appears best when track is studded generously with carbide studs on the outer track bands and scat st
4. 3 Enlarge radius of 4 exhaust port corners to 0 20 b 1mm Figure 1 4 After grinding exhaust port chamfer all sharp edges Raise Exhaust Port to 1 120 Lower Inlet Port to 3 675 below Top Surface of Cylinder below Top Surface of Cylinder Enlarge Radius of 4 Exhaust Port Corners to 0 20 Ki 3 S E 1 h 3 lt k 5 4 3 s DUE E Ce amun m E ms s NW r 1 a 7 D LA H 7 a E 1 RK a L 5 1 1 i 1 1 Enlarge Radius of 2 Bottom Inlet Port Corners to 0 25 Increase Chordal Width of Exhaust Port to 1 460 NF EX IN T por dm t A Fe j Shape of Stock Ports EEN eg Shape of Modified Ports Figure 1 340 S T Modified Stock and Super Modified Cylinder Dimensions 8 Port Enlarge inlet port of cylinder as follows 1 Lower bottom edge of inlet port to a point 3 675 93 35mm below top surface of cylinder Figure 1 DO NOT change top edge or chordal width of inlet port 2 Enlarge radius of 2 bottom inlet port corners to 0 25 6 35mm Figure 1 3 After grinding inlet port chamfer all sharp edges EXHAUST SYSTEM Modification of stock exhaust system is not permitted for modified stock competition CARBURETION Adjust high speed mixtures adjust mixture needles and or replace fixed high speed jets to attain normal coloration of spark plugs CAUTI
5. Remove 0 060 from Inlet Side of Piston Skirt ui pise Shape of Stock Piston Shape of Modified Piston Figure 2 440 S T Modified Stock Piston EXHAUST SYSTEM NOTE When removing parts muffler air intake box etc from snowmobile keep in mind that you are making the machine lighter A certain amount of weight may have to be retained to meet weight limit Remove muffler assembly from snowmobile and modify stock exhaust system as follows A Exhaust Pipe Diverging Cones 1 Cut 1 00 25 40mm from diverging cone of each exhaust pipe directly behind header joint Figure 3 2 Weld header joint to diverging cone of each exhaust pipe Be sure that welds are smooth and do not restrict exhaust 3 Reposition spring hooks on exhaust pipes to give sufficient spring tension Cut 1 00 from Diverging Cone of Each Exhaust Pipe Directly Behind Header Joint and Re weld 17 00 D E A Gut 1 00 from 1 00 ID Converging Cones Center Section Rotate for Best Fit in Snowmobile _ and Re weld Center e ec H 1 Sections J 1 een E e re Cut 1 00 from Modified Center Section Stingers Figure 3 440 S T Modified Stock Exhaust Pipes B Exhaust Pipe Center Sections 1 Cut 1 00 25 40mm from center section at widest part of each exhaust pipe Figure 3 2 Before re we
6. Super Modified ENGINE A Cylinders 1 Exhaust Port Enlarge exhaust port of each cylinder as follows d Raise top edge of exhaust port to a point 1 100 27 94mm below top surface of cylinder Figure 1 DO NOT change bottom edge of exhaust port Square off side edges of exhaust port down to a point directly opposite top of transfer ports while increasing chordal width of port to 1 438 36 00mm Figure 1 Cut a 0 50 12 70mm radius in side edges of exhaust port at a point directly opposite top of transfer ports and continue side edges of port over to bottom edge of port as shown in Figure 1 NOTE Chordal width Figure 1 is straight line distance between side edges of port not following curvature of cylinder wall Change radius of 2 top exhaust port corners to 0 20 5 08mm Figure 1 After grinding exhaust port make a 0 060 1 52mm chamfer to top edge of exhaust port Figure 1 DO NOT chamfer side edges or bc or bottom edge of port Remove sharp edges from exhaust port by lightly rounding cylinder bore edges of port with fine emery cloth Raise Exhaust Port to 1 100 below Top Surface of Cylinder Lower Inlet Port to 3 779 below Top Surface of Cylinder Reduce Boss to Minimum Required to Completely Cover Piston Ring When Piston Is at BDC Bottom Dead Center Cut 4 Inlet Port Corners at a Radius of 0 20 Change Radius of 2 Top Exhaust Port Corners to 0 20
7. lean will cause severe internal richer engine damage DRIVE SYSTEM A Maximum Engine RPM A super modified 340 S T will deliver maximum power when operated at 9 750 to 10 000 RPM Modify and adjust torque converter to increase full throttle engine RPM to this speed B Drive Sheave Clutch Install Drive Sheave Modification Kit D 71711A1 Modify profile of drive sheave ramps to attain correct full throttle engine RPM as recommended in preceding paragraph and desired shift pattern NOTE Clutch modification instructions are supplied with modification kit C Sprockets Snowmobile may require re gearing because of increased horsepower a result of engine and exhaust modification Installation of another driver sprocket may be desired depending upon operating conditions to change top speed of snowmobile MPH and acceleration Refer to Driver Sprocket Chart preceding Sno Twister Hi Performance Tipster NOTICE Sno Twister Hi Performance Tipsters are in numerical order starting with 75 1 If the first copy you receive is example 75 3 and you desire previous Tipster issues 75 1 and 75 2 advise Mercury Marine Publications Dept PO Box 1108 Fond du Lac WI 54935 and give the first number that you received 440 S T MODIFICATION INSTRUCTIONS IMPORTANT Modification of exhaust system and or engine VOIDS your WARRANTY Modification instructions are intended solely for race applicati
8. 3 Change radius of 2 top exhaust port corners to 0 20 5 08mm Figure 1 Enlarge radius of 2 bottom exhaust port corners to 0 50 12 70mm Figure 1 5 After grinding exhaust port make a 0 060 1 52mm chamfer to top and bottom edges of exhaust port Figure 1 DO NOT chamfer side edges of exhaust port 6 Remove sharp edges from exhaust port by lightly rounding cylinder bore edges of port with fine emery cloth Xs s Raise Exhaust Port Lower Inlet Port to to 1 100 below Top 3 779 below Top Surface of Cylinder __ Surface of Cylinder Reduce Boss to Minimum Make a 0 060 Change Radius of 2 Required to Completely TT rTT Chamfer to Top Top Exhaust Port Cover Piston Ring When d Edge of Exhaust Corners to 0 20 d Piston Is at BDC MI Bottom Dead Center Cut 2 Hottom Inlet Port Corners Chamfer to Bottom Edge of Exhaust Port Enlarge Radius of 2 Bottom Exhaust Port Corners to 0 50 F FF Square Off Side Edges of Exhaust Port Shape of Stock Ports While Keeping a Chordal Width of 1 654 Shape of Modified Ports Figure 1 340 S T Modified Stock Cylinder Di mensions B Inlet Port Enlarge inlet port of each cylinder as follows 1 Lower bottom edge of inlet port to a point 3 779 95 99mm below top surface of cylinder Figure 1 DO NOT change top edge or chordal width of inlet port 2 Cut2 bottom inlet port corners at a radius of 0 20 5 08mm Fig
9. Figure 5 3 Weld modified stingers 1 1 8 ID x 0 040 thick approximately x 15 long 28 58mm x 1 02mm x 38 1cm Figure 5 to converging cones Be sure that welds are smooth and do not restrict exhaust Page 5 Snowmobile Tipster No 75 7 CARBURETION A Carburetors Replace stock carburetors Mikuni VM 36 with Mikuni VM 38 carburetors 38mm Carburetors are available thru Mercury Marine see Ordering Information following B High Speed Mixture 1 Fixed high speed jets in the range of No 400 to No 480 depending upon conditions of operation will be required in VM 38 carburetors Fixed high speed jets are available thru Mercury Marine see Ordering Information following 2 Adjust high speed mixtures adjust mixture needles and or replace fixed high speed jets to attain normal coloration of spark plugs CAUTION When in doubt about high speed mixture adjustment ALWAYS select a richer setting Carburetors which are adjusted too lean will cause severe internal engine damage C Ordering Information To obtain ordering information on modified carburetors Mikuni VM 38 and fixed high speed jets No 400 to No 480 contact Mercury Marine Hi Performance Products Department 20 Wisconsin Street Oshkosh Wisconsin 54901 Attention Snowmobile Division Telephone 414 231 9180 DRIVE SYSTEM A Maximum Engine RPM A super modified 440 S T will deliver maximum power when operated
10. D E E LUN T 8 1 1 1 1 I g j AD 4 AT 4 Aa y te 0 e i WA WW NT es rot Lem bc d i dn ab eg D A U Ww d 2 9 T 4 gos o 1 2 M 1 I e v S dad WT GA db i S eh 7 a be i l W D 0 en t Th Gan i mum phu E A 7 3 ia et Up _ Po 8 Beat he rf s 0 1 E UN s E x reis ar mw i SE pn sl n 0 7 d 5 Jm mE DEC s B L 1 em mr Woy que Ri 3 L Ce m i kA An S i mh m T H b ke Em f apes M 1 ch 7 1 e LU NOTICE Sno Twister Hi Performance Tipsters for 1976 are in numerical order starting with 76 1 If the first copy you receive is example 76 3 and you desire previous Tipster issues 76 1 and 76 2 advise Mercury Marine Publications Dept P O Box 1108 Fond du Lac Wi 54935 and give the first number that you received No 76 1 11 26 75 MERCURY MARINE CERTIFIED SNOWMOBILE SPECIFICATIONS 1976 1976 1976 1976 PNE 340 T T x 440 T T 250 S T 340 S T Ignition Min Compressed Head Gasket Thickness Thunderbolt CD Thunderbolt CD 0 7mm Engine Model 6340285 Kasozas zone 34086 No of Cylinders E Engine Displacement EE Bk aos EE Liqui
11. E na j D E EH i bel 0 Kr 8 D 1 utl d 1 y 1 WI 1 d 0 k P 1 J d n t 4 n P P 1 9 1 um k 07 1 1 n 4 D 7 r A 1 Ny 35 by i de 1 d NI d 1 0 dos 1 bw D 7 De 1 0 1 mm WV F hcg cn P Wl W E MERCURY MARINE CERTIFIED SNOWMOBILE SPECIFICATIONS NOTE All Length Measurements Are in Millimeters unless Specified Inches All Volume Is in Cubic Centimeters Conversion Table Below 1974 ENGINE SPECIFICATIONS Engine Manufacturer Kohler 340 S T 440 S T 440 T T 340 S R 440 M X 440 S R Mark TI kanns K3402AX 62644022 KEC440 22 Mork Zeg dE eg t 4 H3JI5 AML ONE m Sa e x 8 E d x 2 19a Engine Displacement 3982 Een RE O S8 Type of Cooling FA A EA ms Fan uM EDI ue es 826 660 leo lan Nd gt ae gt Min Compressed Head 0 95 Gasket Thickness Mag 0 7 J eA Mag I 13050 6300 10x 463 0 10 Jeng Tonon NA i Y e CH il CD gt e The F A 8 8 60 0 Nw Min Compressed Base Gasket Thickness d 0 Volume af Head to Top of Spark Plug Hole 7 14 7 li Depth Top of Cylinder 90 5 o
12. NOTE Use fixed high speed jets which are 3 to 4 jet sizes larger richer than those required for a stock 440 S T DRIVE SYSTEM A Maximum Engine RPM A modified stock 440 S T will deliver maximum power when operated at 9 750 RPM running on to 10 000 RPM Modify and adjust torque converter to increase full throttle engine RPM to this speed B Drive Sheave Clutch Install Drive Sheave Modification Kit D 71711A2 Modify profile of drive sheave ramps to obtain correct full throttle engine RPM as recommended in preceding paragraph and desired shift pattern NOTE Clutch modification instructions are supplied with modification Kit C Sprockets Snowmobile may require re gearing because of increased horsepower a result of engine and exhaust modification Installation of another driver sprocket may be desired depending upon operating conditions to change top speed of snowmobile MPH and acceleration Refer to Driver Sprocket Chart following DRIVER SPROCKET CHART Top Speed of Snowmobile MPH No of Teeth Part Number High MPH D 69757A18 D 69757A17 D 69757A16 x D 69757A15 D 69757A14 D 69757A13 Low MPH 12 D 69757A 12 a Standard factory installed 440 S T driver sprocket BREAK IN PROCEDURE After modifying an S T Snowmobile and prior to racing the engine should be run in at part throttle 50 to 75 power for one hour Operate engine at 110 F to 1709F coolant temperature f
13. TWISTER Mercury Formula 25 Mercury Formula 50 Mercury Formula 50D Castrol Synthetic High Performance Snowmobile Oil NOTE You may want to clamp or wire the fuel lines at the fuel pump ICE STUDS and CARBIDES Carbide wear skegs D 68440 must be installed for racing The ski holes may need to be drilled out and an oversize washer used above the ski to make the carbide fit properly Ice studs D 68441 must be installed on the track A good starting point is to install eleven studs on each side utilizing the holes in the track bars One or two additional rows of eleven can be added in the center band of the track but should be attached to the rubber only not thru the bar Use washers to space the studs up to the 3 8 allowable You may prefer to set tne steering in the low effort position since the carbides increase the steering effort considerably See your Operation and Maintenance Manual SLIDER TRACK ADJUSTMENT The track must be adjusted for proper tension as outlined in your Owners Manual The track will run smoother if the drive sprockets are lubricated with grease STP works well Most of the side load is taken out through the wear plates inside the tunnel so be sure to lubricate the edge of the track As outlined in your Owners Manual handling oversteer and understeer can be adjusted We found that for best weight transfer the rear springs should be set soft and the front springs in the 34 position Set yours up and t
14. Intake Ports 28 5410 30 3310 24 0 5 22 5 Reed Valve Reed Valve Reed Valve A Assembly 2 240gr 10gr 310gr 10gr 335gr 1096 240gr 10 307gr 1095 3076 491 680 gt Overall Height of Piston 67 51 55 07 56 717 5 84 178 71425 D 246 D e C a TE Ring Type Dykes Keystone Dykes Keystone Rectanguler L amp Reciangula Rectangular Rectangular cation m Ring Thickness 20 20 08 25 08 2 02 08 2 03 08 1 50 1801 Crankcase Face to Center 179 9 70 04 5 70 04 5 70 0 2 58 0 1 70 23 2 70 23 2 1 Piece 0 of Crankshaft A 4 W lt l o Main Bearing Type Sealed Ball Sealed Ball Sealed Ball Sealed Ball Sealed Ball Sealed Bail Sealed Ball Sealed Ball gt Muffler Make Merc Donaldson 3 DBA Level 82 2 822 jE 8 A Head Pipe Length 985 Ing 167 6 2 Y Manifoid 57 7 6 25 25 1270 Piston TDC CARBURETOR Make Model No Mikuni VM 36 Mikuni 36 34RS Mikuni 36 44RS_ Mikuni VM 36 ms Ven turi Smallest 136 0 Diameter in Throat Walbro WDA Walbro W RA 3 m GA s Za tal 8 Throttle Bore Largest Dia EE Lek uis e 2 96 eege ss 7 Ys DRIVE CLUTCH Arctic Cat Arctic Cat Make Model No Comet 100C Le D61 XX XX 062 Salsbury 850 3000080
15. Mercury Salsbury 850 m VIRIS Y uL 3200 RPM TO iain Plain ja LL Ri e CE DRIVEN CLUTCH Spring Wire Diameter 192 D E E EI E L gt a a a OF Ee e Sege eege weie ee nn Chassis Model 66 69 70729 70729 72006 66602 70238 68345 66011 Supenion C E Swing Frame 3 252 000263 008 43 M Joses siiis eet sees Rubber G rouser Rubber TRACK Make Goodyear Goodyear Goodyear Goodyear Rubber Rubber Rubber Rubber Steel Bars Bars Steel Steel Bars Material LU us Length OD 2820 281644125 30724 30724 33274 Track Drive Sprocket Teath a mI CHAINCASE Standard Drive Sprocket No of Teeth Standard Driven Sprocket Nova Teen eg ees Optional Drive Sprockets No of Teeth 13 14 16 12 13 15 16 17 12 13 14 16 17 12 13 14 15 16 18 Optional Driven Sprockets No of Teeth Snowmobile Weight Pounds 360 10 am 1 13 14 16 17 8 12 13 14 15 18 17 12 13 14 15 17 18 caes ape 28 36 38 40 28 34 38 40 28 34 38 40 34 36 38 40 28 34 38 40 e Mi CH gt E gt METRIC CONVERSION 1mm millimeter 0 0394 inch 1 gr gram 0 04 oz 1 cubic centimeter 0 06 cu in 1 Ib pound 0 4536kg kilogram N A Not Applicable 2 0 4 Spacers 06 Thic
16. To obtain and maintain ultimate snowmobile performance proper clutch operation is a must in maintaining peak engine operating RPM 1 Use drive belt D 57 74294 identified by white patch on belt cover 2 250 S T adjust driven sheave spring preload to achieve 9200 to 9500 engine RPM at W O T acceleration 3 340 S T 440 S T adjust driven sheave spring preload to achieve 9250 to 9500 engine RPM at W O T acceleration 4 Frequently disassemble clean and inspect drive clutch assembly once every race day is recommended IMPORTANT To prevent scarring or chipping the inside diameter of the cover bushing TAKE PARTICULAR CARE to keep cover SQUARE on shaft prevent cocking and binding as cover is removed and or installed This task is made somewhat easier if the complete drive clutch is removed from the engine before disassembly During each inspection be certain to inspect the bushings in all of the roller assemblies Failure to recognize and replace rolier assemblies with worn bushings will lead to premature ramp destruction NOTE Construction and use of the simple tool sketched below is an unbelievable time saver not to mention an aid to your sanity when removing and installing the roller assemblies Round the Edges Insert Tang A 1 25 4mm Approx between Roller Arm and Twist Tool 3 8 9 5mm to Spread Arms BW Material 570 SCALE 1 1 3 16 4 8mm 580 amm Thick Steel
17. and give the first number that you received SET UP INFORMATION Stock 1976 Model 250 340 440 S T Snowmobiles IGNITION TIMING Standard ignition timing for each model as specified in the S T Operation and Maintenance Manual MUST BE ADHERED TO Advancing ignition timing beyond the recommended specification will gain absolutely nothing and could cause serious engine damage SPARK PLUGS Standard spark plugs Champion QN 19V MUST BE USED FOR RACING Champion N 55G plugs which are easier to read may be used to determine correct carburetor jetting ONLY CYLINDER HEAD SQUISH CHAMBER CLEARANCE A MINIMUM of 030 0 76mm clearance must be maintained between cylinder head and piston dome heads torqued to 225 in lbs 259kg cm after engine warmup to a minimum of 110 F 439 C When re using head gaskets check squish chamber clearance as follows 1 Place a piece of L shaped soft wire solder through the spark plug hole to the cylinder wall 2 Rotate engine over TDC 3 Remove and measure flattened section of wire solder COOLING SYSTEM When installing cylinder heads a thin film of GE Silicone Sealer should be used on both sides of the cylinder head gaskets f coolant leakage should occur at cylinder head mounting studs clean the mounting hardware and apply GE Silicone Sealer to the stud threads and bosses on the cylinder heads in extreme cold temperatures it may be n
18. and prior to racing the engine should be run in at part throttle 50 to 7596 power for one hour Operate engine at 1109F to 1709F coolant temperature for Break In and all operation thereafter Sno Twister Hi Performance Tipster Cum NOTICE Sno Twister Hi Performance Tipsters for 1976 are in numerical order starting with 76 1 If the first copy you receive is example 76 3 and you desire previous Tipster issues 76 1 and Fond autas No 76 4 12 1 75 340 S T MODIFICATION INSTRUCTIONS IMPORTANT Modification of exhaust system and or engine VOIDS your WARRANTY Modification instructions are intended solely for race applications CAUTION Modify engine exhaust system and carburetion EXACTLY as instructed following ANY DEVIATION from SPECIFIED DIMENSIONS or MODIFICATION of PARTS NOT MENTIONED WILL DECREASE PERFORMANCE and could result in severe engine damage Modifying 340 S T from Stock to Modified Stock CYLINDERS A Exhaust Port Enlarge exhaust port of each cylinder as follows 1 Raise top edge of exhaust port to a point 1 100 27 94mm below top surface of cylinder Figure 1 DO NOT change bottom edge of exhaust port 2 Square off side edges of exhaust port while maintaining a chordal width of 1 654 42 00mm Figure 1 NOTE Chordal width Figure 1 is straight line distance between side edges of port not following curvature of cylinder wall
19. at 9 500 to 9 750 RPM Modify and adjust torque converter to increase full throttle engine RPM to this speed B Drive Sheave Clutch Install Drive Sheave Modification Kit D 71711A1 Modify profile of drive sheave ramps to obtain correct full throttle engine RPM as recommended in preceding paragraph and desired shift pattern NOTE Clutch modification instructions are supplied with modification kit C Sprockets Snowmobile may require re gearing because of increased horsepower a result of engine and exhaust modification Installation of another driver sprocket may be desired depending upon operating conditions to change top speed of snowmobile MPH and acceleration Refer to Driver Sprocket Chart preceding 7 1 n w M M E a D lt 1 Ait n gt ate bg m gt Y p we dini WII Y 1 E e a A LI 4 4 A d uw 4 I Ap Ks Buu iue ENT sudes E 0 V etii Se g5 ER e sv 5 wet 49M y 44 Uh anu e Ws u w 0 0 x D dai eed o k 1 Ae e o do rat Ld NOTICE Sno Twister Hi Performance Tipsters are in numerical order starting with 75 1 If the first copy you receive is example 75 3 and you desire previous Tipster issues 75 1 and 75 2
20. lower bulkhead to crossmember with 9 steel rivets D 17 74671 Figure 1 The Mercury Marine Limited Warranty is not extended to snowmobiles that are used for racing Cost of this reinforcement is to be borne by the owner a aw T a EA Se d M nane ie AT sa rl Mos p Ni EN ULI ILU i 4 MAT JI ba ba A dun DMD i 1 H gunk T E HA m W er NG
21. ru NEUE 7 4 5 re p ZS P A Ze u b T _ hM H Ai d A Sno Twister Hi Performance Tipster NOTICE Sno Twister Hi Performance Tipsters are in numerical order starting with 75 1 If the first copy you receive is example 75 3 and you desire previous Tipster issues 75 1 and 75 2 advise Mercury Marine Publications Dept P O Box 1108 Fond du rn Lac WI 54935 and give the first number that you received N 0 75 9 1 2 1 8 74 340 S T and 440 S T DRIVE SHEAVE RAMPS suggested Dimensions for SUPER MODIFIED Ramps As a result of factory testing Mercury has designed a drive sheave ramp profile suitable for 340 S T and 440 S T Super Modified Snowmobiles see drawing below This ramp profile is intended to be used with green compression spring and optional weights 0146 135 for 340 S T and 0146 123 for 440 S T Green compression spring an assortment of weights a set of blank ramps hardened and an instruction sheet are included in Drive Sheave Modification Kit D 7171141 e e _ m a 1 5 5 1 B Centerline of Bolt 3 e Hole 14 Profile of ME Hamp Ts Profile nf Super Modified Ramp v x ACTUAL SIZE Suggested Dimensions for 340 S T and 440 S T Super Modified Drive Sheave Ramps z u oma s amp Hal 5 Du I 0 MN UT CN
22. to 1 690 9 EUN SC ee Shape of Stock Ports E Shape of Modified Ports Figure 1 440 S T Modified Stock and Super Modified Cylinder Dimensions Page 2 Snowmobile Tipster Na 75 7 2 Inlet Port Enlarge cylinder inlet port as follows a Lower bottom edge of inlet port to a point 3 850 97 79mm below top surface of cylinder Figure 1 3 b Raise top edge of inlet port to a point 2 470 62 74mm below top surface of cylinder Figure 1 c Increase chorda width of inlet port to 1 770 44 96mm Figure 1 d Enlarge radius of 2 bottom inlet port corners to 0 75 19 05mm Figure 1 e Enlarge radius of 2 top inlet port corners to 0 20 5 08mm Figure 1 f After grinding inlet port chamfer all sharp edaes Remove 0 080 rp enge from Inlet Side B Piston of Piston Skirt Remove 0 080 2 03mm from inlet side of Kg piston skirt Figure 2 After cutting piston skirt Shape of Stock Piston i remove all sharp edges from skirt Shape of Modified Piston NOTE Inlet side of piston is side opposite Figure 2 440 S T Modified Stock and exhaust mark on piston dome Super Modified Piston EXHAUST SYSTEM Modification of stock exhaust system is not permitted for modified stock competition CARBURETION Adjust high speed mixtures adjust mixture needles and or replace fixed high speed jets to obtain normal coloration of
23. 7 64817 or equivalent with the backing washers o P ANTRO o 1 we TY Angel 2 81 777 FPL LIFE Number 76 13 BU LLEI IN SNOWMOBILES Date 12 22 75 EE cimcuLATE SERVICE MGR PARTS MGR MECHANICS TO MERCURY SNOWMOBILES with ARCTIC DRIVE CLUTCH Internal Drive Clutch Component Information Place in Your Service Bulletins Binder Stock Drive Clutch Component Chart 340 S T 440 S T 340 T T 440T T 250 S T 340 S T 440 S T 4207500 4206250 4347125 4347124 4495560 4495559 4349324 Moursiearonive urewcoven JJ me e color Red Black na Rea Black C nei Gram Weight _ 5958 _ Outside Diameter Joe Josee Joe nes Joen Wan 0 _ Mercury Part No 071717 ozme o D74225 oz banalen DRIVE CLUTCH RAMPS AE rur 1 None None None Drawing of Ramp Profile Figure CO Figure3 Figure4 Figure5 MeruryPartNo 6 OO o 71496 ba D 74124 _ _ pz5 7 107517 1 Optional Clutch Ramps D 74857A 1 Figure 2 are available for trail riding 2 A few 1976 Mode 340 S T snowmobiles were shipped from the factory with INCORRECT drive clutch weights Weights stamped 0146 135 D 71737 MUST BE INSTALLED in these clutches ACTUAL SIZE ACTUAL SIZE ACTUAL SIZE Figure 1 D 71496 Drive Clut
24. Conversion 1976 1976 1976 250 S T 340 S T 440 S T CARBURETOR Make Model No Mikuni VM36 34 Mikuni VM34 7 uni 4 gt Venturi Smallest Diameter it 1 7 4 m m i in Throat m Se Yes Ye EN x L 2 ase a Arctic XXXX 1 Arctic XXXX 088 Arctic XXXX 089 mm 4000 RPM 4000 RPM 4000 RPM Green Vereen VGem 7 EL O0 1 n 37573 280 1927 005 250 Ka 4 375 Z50 Drive Clutch Spring Free Length No of Turns 5 gt 7 Drive Clutch Spring 2 375 2 375 D40 2 375 040 Outside Diameter s Arm Roller Weight 28 34 209 495220 e Drive Clutch Roller 470 07 470 A70 O10 I Diarneter DRIVEN CLUTCH Make Model No Arctic XXXX 015 Arctic XXXX 015 Arctic XXXX 015 Quantity Driven Clutch 0 1 TT a s Springis Spring Wire Diameter 1 5 005 156 005 158 No of Turm 5 es Driven Clutch Spring Free Length 5 1 5 00 250 Rame Angle w5x5 zg 5 Suspension Slide Rail 60 Slide Rail Slide Rail Slide Rall 1 Overali Vehicle Length 98 44 500 89 44 89 875 2507 2 89 875 250 89 875 250 00 250 82 875 250 82 875 250 82 875 250 Chas
25. ENGINE A Cylinders 1 Exhaust Port Enlarge exhaust port of each cylinder as follows a Raise top edge of exhaust port to a point 1 100 27 94mm below top surface of cylinder Figure 1 DO NOT change bottom edge of exhaust port b Increase chordal width of exhaust port to 1 772 45 00mm Figure 1 NOTE Chordal width Figure 1 is straight line distance between side edges of port not following curvature of cylinder wall c Change radius of 2 top exhaust port corners to 0 13 3 30mm Figure 1 Enlarge radius of 2 bottom exhaust port corners to 0 50 12 70mm Figure 1 After grinding exhaust port make a 0 060 1 52mm chamfer to top and bottom edges of exhaust port Figure 1 DO NOT chamfer side edges of port f Remove sharp edges from exhaust port by lightly rounding cylinder bore edges of port with fine emery cloth p Raise Exhaust Port to 1 100 Lower Inlet Port to 3 829 below Top Surface of Cylinder below Top Surface of Cylinder Change Radius of 2 Top Exhaust Port Make a 0 060 Corners to 0 13 Chamfer to Top Edge of Exhaust Reduce Boss to Minimum Required to Completely Cover Piston Ring When Piston 5 at BDC Cut 4 Port Bottom Dead Center Port Corners at a Hadius of 0 13 NT H X D NM Make a 0 060 e Kaz N S S Enlarge Radius of NS Se Bottom Edge of we Exhaust Port 2 Bottom Exhaust Mak 060 Ch
26. Make a 0 060 Chamfer to Top Edge of Exhaust Port t L This Point on Side I Lx Edges of Exhaust A N NN V Fort Must Be Cut a 0 50 Radius in Make a 0 060 Chamfer S NN Bmecuy Opposite Side Edges of Exhaust to Bottom Edge of Inlet Port 7 0 Port at a Point Directly Ports Opposite Top of Transfer Ports and Continue Square Off Side Edges of Exhaust Side Edges of Port Port Down to a Point Directly Opposite 35 over to Bottom Edge Top of Transfer Ports While Increasing Chordal Width to 1 438 ne Shape of Stock Ports Shape of Modified Ports Figure 1 250 S T Modified Stock Cylinder Dimensions 2 Inlet Port Enlarge inlet port of each cylinder as follows a Lower bottom edge of inlet port to a point 3 779 95 99mm below top surface of cylinder Figure 1 DO NOT change top edge or chordal width of inlet port b Cut 4 inlet port corners at a radius of 0 20 5 08mm Figure 1 Reduce boss at top edge of inlet port to a minimum Figure 1 Boss must be large enough to completely cover piston ring when piston is at BDC bottom dead center d After grinding inlet port make a 0 060 1 52mm chamfer to bottom edge of inlet port Figure 1 DO NOT chamfer side edges or top edge of port e Remove sharp edges from inlet port by lightly rounding cylinder bore edges of port with fine emery cloth IMPORTANT DO NOT POLISH transfer passages B Ignition Timing Retard ig
27. NT During break in period a slightly rich high speed mixture adjustment is advisable Use a good premium gasoline and Merc Snowmobile Oil when mixing gas oil Make it a slightly richer mixture for the first few hours of running until piston rings have seated properly Run at high RPM for short durations only avoid sustained full throttle operation and prolonged operation at a constant throttle setting Check spark plugs often to ensure that engine is not overheated w Become familiar with the feel of the sled clutch engagement shifting sound etc and its handling characteristics This is very important for later testing RACE PREPARATION BASIC Cleaning and Inspection After the break in period is completed thoroughly clean the snowmobile Visually check the engine and chassis for worn or broken parts Remove cylinder heads and inspect head gaskets pistons rings and cylinders for excess wear cracks chipped chrome etc Repair or replace components as necessary Check piston fit and ring clearances end gap and side clearance Secure exhaust headers to cylinders using safety wire or bearing mount type Loctite on hex screws Check ignition timing should be 100 BTDC 21749 Check ski alignment parallel measuring front and rear of skis For easier slower steering use the tie rod attaching hole closest to the steering shaft Try both positions for your preference Check track and suspension Track tension
28. O Box 1108 Fond du pe c A Lac WI 54935 and give the first number that you received 1975 SNO TWISTER 340 S T 440 S T COMPETITION SETUP INFORMATION POSSESSION Possession of a Sno Twister well in advance of the 74 75 racing season can be a very big assist It gives the driver ample time to get acquainted with the sled and to properly break it in before entering competition INITIAL SETUP After receiving a Sno Twister you may want to thoroughly check the engine assembly and possibly even disassemble it completely to familiarize yourself with all the parts and to make certain that all components and their assemblies meet with your satisfaction If so rebuild the engine with the care and precision that a surgeon would use It brings results Pay special attention to all nut and bolt torque specifications Use Loctite on all bolts that secure trigger and stator to crankcase When assembling cylinders to crankcase make sure that the transfer ports are lined up correctly with no gasket overhang Make certain that the cylinder head dome is centered directly over the cylinder Check carburetor float levels and adjust high and low speed mixture screws to specifications e Reinstall engine assembly then check torque converter alignment drive belt tension drive chain tension track tension and alignment and adjust to specifications refer to Owner s Manual BREAK IN PERIOD IMPORTA
29. ON When in doubt about high speed mixture adjustment ALWAYS select a richer setting Carburetors which are adjusted too lean will cause severe internal engine damage DRIVE SYSTEM A Maximum Engine RPM A modified stock 340 S T will deliver maximum power when operated at 8 750 to 9 000 RPM Modify and adjust torque converter to increase full throttle engine RPM to this speed B Drive Sheave Clutch Install Drive Sheave Modification Kit D 71711A1 Modify profile of drive sheave ramps to attain correct full throttle engine RPM as recommended in preceding paragraph and desired shift pattern NOTE Clutch modification instructions are supplied with modification kit C Sprockets snowmobile may require re gearing because of increased horsepower a result of engine modification Installation of another driver sprocket may be desired depending upon operating conditions to change top speed of snowmobile MPH and acceleration Refer to Driver Sprocket Chart following DRIVER SPROCKET CHAHT Top Speed of Snowmobile MPH No of Teeth High MPH D 63573 D 64131 0 81 D 64684 D 68439 Low MPH x D 69757 12 8 Standard factory installed 340 S T driver sprocket JA cs 5 T Pears H Modifying 340 S T from Stock to Super Modified ENGINE A Cylinder 1 Exhaust Port Enlarge cylinder exhaust port as outlined in Modifying 340 S T from Stock to Modified Stock pre
30. S Serial No 4349537 and Below IMPORTANT ALL 1976 Model 250 S T already are equipped with the balancer ALL 1976 Mercury Sno Twister Snowmobiles MUST BE equipped with a balancer steel disc 156 3 96mm thick by 5 250 13 34cm diameter between the rewind starter cup and lower pulley The balancer D 75961 stabilizes the crankshaft and prevents excessive vibration of the drive clutch thereby improving the life of drive clutch components IMMEDIATELY notify owners of the above specified Sno Twister Snowmobiles that this balancer MUST BE INSTALLED installation instructions following IMPORTANT A simple visual inspection via the water pump belt channel in the bell housing can verify whether or not the balancer has been installed Order the required quantity of balancers and 4 screws for each balancer from your parts distribution source Credit for the balancers screws and 0 3 hrs labor per snowmobile will he issued upon receipt of a completed warranty claim One warranty claim listing individual CHASSIS Serial Nos may be used to cover service to all snowmobiles C 75961 Balancer 1 per Snowmobile C 10 75967 Screws 4 per Balancer INSTALLATION INSTRUCTIONS Remove rewind starter assembly 2 Remove 4 screws which secure rewind starter cup and lower pulley to rotor RETAIN the 4 lockwashers from the screws and discard the screws 3 Install balancer between lower pulley and starter rewind cup IMPORTANT Failure to us
31. S T Chassis Serial No 4349324 and Above CHASSIS FRONT CROSSMEMBER Mercury Marine has received a few reports of the chassis front crossmember D 74553A2 failing on 1976 Model Sno Twister snowmobiles that have been raced The crossmember failure is occuring just outside of engine mounting tabs either side ALL CROSSMEMBERS MUST BE INSPECTED and REINFORCED IMMEDIATELY before further operation of snowmobile Reinforce crossmember as follows 1 Remove 11 rivets which secure lower bulkhead to crossmember Figure 1 If any cracks in crossmember are evident weld as necessary before installing reinforcing steel strap 2 Position a reinforcing steel strap 11 gauge 0 1196 cold rolled steel 1 00 x 30 50 between lower bulkhead and crossmember Figure 1 g 11 Gauge 0 1196 Cold Rolled Do Not Reinstall Steel Strap 1 00 x 3050 1 This Rivet di Do Not TT Reinstall gt This Ba Rivet fer 9 Welds as Shown 1 8 Wide x 1 Long d Weld Both Ends 1 8 Wide x Long Bulkhead Figure 1 Reinforcing Crossmember Viewed from Underside 3 Securely weld steel strap to crossmember ONLY at locations shown in Figure 1 IMPORTANT Outer rivets one each side Figure 1 will not be reinstalled therefore DO NOT drill a rivet hole thru steel strap at these locations 4 Using rivet holes in lower bulkhead as a guide drill 9 rivet holes 3 16 thru reinforcing steel strap 5 Secure
32. SENVICE 7771 7 o Date 12 1 75 SNOWMOBILES PARTSMGR MECHANICS GASOLINE OIL RECOMMENDATIONS ALL MERCURY SNOWMOBILES Attach Bulletin Reference Sticker to Page 1 6 of Your Snowmobile Service Manual Place in Your Service Bulletins Binder IMPORTANT Supersedes all information previously published on gaso line oil recommendations Service Manual Operation and Maintenance Manuals Snowmobile Service Bulletins and fuel Warning Tags Posters Fan Cooled and Free Air Models Recommended Oil s D WS E E Ratio 1 Gasoline 2 Gasoline 3 Quicksilver Snowmobile Regular Quicksilver Formula 25 Leaded 100 130 Quicksilver Formula 50D Minimum 86 AvGas Quicksilver Formula 50 Average Octane 1 Ratio of 25 1 is required for the first one tank full during engine Break In period and or for Severe Service operation Refer to Operation and Maintenance Manual for Severe Service definition 2 For 1975 Model 440 T T Below CHASSIS Serial No 4210250 use PREMIUM UNLESS ignition timing is retarded from 095 BTDC to 080 BTDC 3 For Racing use 100 130 AvGas and retard ignition timing from 100 BTDC to 080 BTDC For Trail Ride use PREMIUM and retard ignition timing from 100 BTDC to 060 BTDC Liquid Cooled Models 0 7 Liquid Cooled ecommended Oil s Ratio Quicksilver Formula 50 ENE Quicksilver Snowmobile Oil 100 130 AvGas Quicksilver F
33. a guide however a proper plug check is the only way to get spot on for racing A Champion N55G plug is easier to read and is suitable for racing After 100 full throttle speed run the correct fuel air mixture will cause plug electrode to have a light chocolate brown color must never appear whitish grey BELOW 2000 ELEVATION 2000 to 4000 ELEVATION Temperature Jet Size Subtract 10 from the jet sizes listed on left Above 309 290 to 300 0 309 320 to 330 Below 09 330 to 360 If your Mercury dealer doesn t have jets try any dealer stocking Mikuni carburetor parts all else fails a 53 drill 059 dia corresponds to a 320 jet and a 1 16 drill 0625 dia corresponds to a 340 jet Move jet needle to richer position by one notch i e the retaining clip should be moved to the fourth 4 notch from the top of the jet needle DRIVE SHEAVE 1 Inspect clutch and lube per instructions in the Owners Operation and Maintenance Manual C 90 68019 2 Check engagement RPM and adjust if necessary 3 Use an accurate tachometer to check engagement speed USSA says 4000 RPM max OVER n r r rr A SNO TWISTER TIPSTER DRIVEN SHEAVE 1 Check alignment per the manual 2 Setspring preload at 2 full cams 3 US A NEW BELT 4 Adjust belt tension per the manual FUEL OIL Use a 20 1 fuel oil mix Only the following oils are known to be satisfactory for SNO
34. ack may dictate 4 Check tightness of all fasteners regularly before each race particularly bolts that secure the ski pivot saddle to the leaf spring assembly and bolts which secure the ski assembly to the spindle TETHER SWITCH Obtain and install a race proven Safety Tether Switch Type of switch and mounting location are strictly driver preference Safety Tether Switch IS NOT available from Mercury Marine IMPORTANT To prevent accidentally stopping the engine during a race we suggest disconnecting the emergency stop switch red located on the throttle control Remove orange wire from No 1 position on terminal block TRACTION DEVICES 1 Carbide insert wear skeg Mercury Marine Part No D 68440 1 on the skis are a MUST for racing 2 The following stud patterns are typical of installations that performed very well on hard pack and ice NOTE Patterns shown are viewed from the bottom of the track rear to front 440 S T KEY X Merc Carbide Stud Part No D 71926 22 pcs in pkg Super Stud Z Merc Scat Stud Part No D 71925 22 pcs in pkg Kangaroo 134 x 5 8 bite FRONT Scat Stud on T 77 Fa MT Carbide Stud on every bar alternating from side every Sth to side 44 pcs required bar LEFT side only Scat Stud with spacer underneath to achieve 3 8 11 pcs 9 5mm maximum height allowed Attach to required track not on bar alternately after every 4th track bar on c
35. and alignment suspension cross shafts wear bending lubrication shock absorbers dampening leakage idler wheels wear and free bearing movement slide wear bars and chassis rub strips Check all nuts and bolts for wear and proper torque Repair or replace parts as necessary Chaincase Clean and inspect chain sprockets jackshaft and bearings Check brake assembly cam pin and pucks for wear free floating and correctly adjusted RACE PREPARATION FINAL Check electrica wiring Disconnect emergency stop switch red switch on throttle control from terminal block located behind dash Be sure that ground wire from CD mounting base to engine is secure and in good condition Red wire from electronic pack connects to PTO side coil white wire connects to coil on rewind side Make certain that CD wiring connectors are coupled securely Install a race proven ignition safety stop switch tether switch to suit rider Check and adjust carburetion re check carburetor float levels Adjust high speed mixture needles as outlined in Owner s Manual to suit conditions temperature and elevation that will be encountered Synchronize throttle slides and adjust idle speed making sure full throttle operation is attained and throttle cable moves freely Check all fuel lines and hoses Be positive that the lines are secure on fittings and not pinched or crimped Check exhaust system Inspect for cracks broken parts and missing coupler spr
36. arter t EL Port Corners to IN te a 001 amfer to i Bottom Edge of Inlet Port 0 50 increase Chordall Width of Increase Chordal Width of Inlet Port to 1 772 Exhaust Port to 1 772 1 aa ef od S d r J Shape of Stock Ports Shape of Modified Ports Figure 1 440 S T Modified Stock Cylinder Dimensions 2 Inlet Port Enlarge inlet port of each cylinder as follows a Lower bottom edge of inlet port to a point 3 829 97 26mm below top surface of cylinder Figure 1 DO NOT change top edge of port Increase chordal width of inlet port to 1 772 45 00mm Figure 1 Cut 4 inlet port corners at a radius of 0 13 3 30mm Figure 1 d Reduce boss at top edge of inlet port to a minimum Figure 1 Boss must be large enough to completely cover piston ring when piston is at BDC bottorn dead center e After grinding inlet port make a 0 060 1 52mm chamfer to bottom edge of inlet port Figure 1 DO NOT chamfer side edges or top edge of port f Remove sharp edges from inlet port by lightly rounding cylinder bore edges of port with fine emery cloth W p IMPORTANT DO NOT POLISH transfer passages B Pistons NOTE Inlet side of piston is side opposite exhaust mark on piston dome Remove 0 060 1 52mm from inlet side of each piston skirt Figure 2 After cutting piston skirt remove sharp edge from skirt by cutting a 005 13mm radius on edge
37. awing the bolt head or washer deeply into the track usually will result in premature loosening of stud and or tearing of track fabric Optional Spacer Sno Twister Hi Performance Tipster amm NOTICE Sno Twister Hi Performance Tipsters are in numerical order starting with 75 1 If the first copy you receive is example 75 3 and you desire previous Tipster issues 75 1 and 75 2 advise Mercury Marine Publications Dept P O Box 1108 Fond du Lac WI 54935 and give the first number that you received No 75 6 11 22 74 340 S T MODIFICATION INSTRUCTIONS IMPORTANT Modification of exhaust system and or engine VOIDS your WARRANTY Modification instructions are intended solely for race applications CAUTION Modify engine exhaust system and carburetion EXACTLY as instructed following ANY DEVIATION from SPECIFIED DIMENSIONS or MODIFICATION of PARTS NOT MENTIONED WILL DECREASE PERFORMANCE and could result in severe engine damage Modifying 340 S T from Stock to Modified Stock CYLINDER A Exhaust Port Enlarge exhaust port of cylinder as follows 1 Raise top edge of exhaust port to a point 1 120 2 amp 45mm below top surface of cylinder Figure 1 DO NOT change bottom edge of exhaust port 2 Increase the chordal width of exhaust port to 1 460 37 08mm Figure 1 NOTE Chordal width Figure 1 is straight line distance between side edges of port not following curvature of cylinder wall
38. ceding 2 Inlet Port Enlarge cylinder inlet port as outlined in Modifying 340 S T from Stock to Modified Stock preceding B Ignition Timing Retard ignition timing full advance from 0 100 BTDC to 0 080 BTDC 2 54mm to 2 03mm EXHAUST SYSTEM A Exhaust Pipe Center Section 1 Cut 4 5 11 43cm from center section of each exhaust pipe Figure 2 2 Before re welding exhaust pipes position pipes in snowmobile and rotate sections to attain best fit 3 Weld sections of exhaust pipes together Be sure that welds are smooth and do not restrict exhaust B Exhaust Pipe Stinger 1 Cut production stinger from each exhaust pipe NOTE Converging cone of exhaust pipes may have to be cut back slightly so that inside diameter ID of cones are enlarged to 1 25 4mm same ID as replacement stinger 2 Weld modified stingers 1 ID x 0 040 thick approximately x 10 5 long 25 4mm x 1 02mm x 26 67cm Figure 2 to converging cones Be sure that welds are smooth and do not restrict exhaust Converging Cones Rotate for Best Fit in Snowmobile and Re Weld Center Sections Modified Stingers Figure 2 340 S T Super Modified Exhaust Pipes CARBURETION Adjust high speed mixtures adjust mixture needles and or replace fixed high speed jets to achieve normal coloration of spark plugs CAUTION When in doubt about high speed mixture adjustment ALWAYS select a setting Carburetors which are adjusted too
39. ch Figure 2 D 74857A1 Drive Figure 3 D 74123 Drive Clutch Hamp Profile 1975 340 S T amp Clutch Ramp Profile Trail Ramp Ramp Profile 1976 340 T T 440 S T for 1975 340 S T amp 440 S T OVER ACTUAL SIZE ACTUAL SIZE ACTUAL SIZE Figure 4 D 74124 Drive Clutch Figure 5 D 75908 Drive Clutch Figure 6 D 75177 Drive Clutch Ramp Profile 1976 440 T T Ramp Profile 1976 250 S T Ramp Profile 1976 340 S T amp 440 S T Drive Clutch Accessories A 1975 1976 1976 1976 1976 Drive Clutch Modification 9 pma 1 Drive Clutch Trail Ride Kit N A Not Available Drive Clutch Weight Chart 0146 175 cr 5 Red 0 437 D 71735 7 0146 135 1 2 3 OO Black 21737 ore SC 9146 DG White 146 106 0 Rea mm emm 71717 3 O Decrease BE 784 9146 105 f _ Black Engine RPM Heavy 8 8009 0146 286 2 Yellow D Six of these elo ts are included in Drive Clutch Modification Kit p 7 171 1A T 2 Six of these weights are included in Drive Clutch Modification Kit D 71711A2 Six of these weights are included in Drive Clutch Elevation Kit D 71712A1 4 Six of these weights are included in Drive Clutch Elevation Kit D 71712A2 5 Six of these weights are included in Drive Clutch Elevation Kit D 71716A1 6 Six of these weights are included in Drive Clutch Elevation Kit D 74124A 1 Fuli Throttle Engine RPM
40. d E om on x Do 7 S _ 86 0 7 rnm Min Compressed Base Gasket Thickness Tj Volume of Head to Top of 21 7cc Head Volume w Spark 18 5 1 0cc Plug on a Flat Plate ke ccce 109 0 0 5mm 108 0 0 5mm Spark Plug Hole Vertical 310 0cc 3100cc 305 00 305 Overall Length of Cylinder 109 0 0 5mm Cylinder Bore Material Chrome Plated Alum Chrome Plated Alum Chrome Plated Alum Depth Top of Cylinder to 92 5 1 0mm 925 10mm B 33 0 1 Bottom of Intake Port Depth Top of Cylinder to Top of Exhaust Port Depth Tap of Cylinder to 47 3 1 2mm Width of Transfer Ports 8424 1 0 14 1 1 0mm 33 8 1 0 12 8 1 0mm 420 08mm Langg 400 08mm 1 Height of Exhaust Port Including Chamfer Height of Exhaust Port Excluding Chamfer 33 0 28 7 1 2mm 29 5 1 2mm 47 3 1 2mm 465 6 12 46 5 1 2mm 27 7 1 0 10 7 1 0mm 32 3 1 0 12 5 1 0mm 44 0 0 5mm 270 12mm 27 0 1 2mm 31 2 1 2mm 30 5 1 2mm 265 0 7mm 26 5 0 7mm e 42 0 0 5mm 30 7 0 7mm 300 32 0 0 5mm 42 0 Port Top Wide Part O Port Bottom Narrow Part i Height of Intake 24 5 71 Port Inciuding Chamfer 24 0 0 7mm 28 0 0 5mm 35 0 0 5mm 13 5 1 0mm 30 5 0 9mm 5 Height of intake Port Exclu
41. d fixed high speed jets Adjust high speed mixture replace fixed high speed jets to achieve normal coloration of spark plugs NOTE Use fixed high speed jets which are 3 to 4 jet sizes larger richer than those required for a stock 340 S T DRIVE SYSTEM A Maximum Engine RPM A modified stock 340 S T will deliver maximum power when operated at 9 750 RPM running on to 10 000 RPM Modify and adjust torque converter to increase full throttle engine RPM to this speed B Drive Sheave Clutch install Drive Sheave Modification Kit D 71711A2 Modify profile of drive sheave ramps to obtain correct full throttle engine RPM as recommended in preceding paragraph and desired shift pattern NOTE Clutch modification instructions are supplied with modification kit C Sprockets Snowmobile may require re gearing because of increased horsepower a result of engine and exhaust modifications Installation of another driver sprocket may be desired depending upon operating conditions to change top speed of snowmobile MPH and acceleration Refer to Driver Sprocket Chart following DRIVER SPROCKET CHART No of Teeth D 69757A18 D 69757A17 D 69757A16 D 69757A15m D 69757A14 D 69757A13 D 69757A12 High MPH Low MPH m Standard factory installed 340 S T driver sprocket BREAK IN PROCEDURE After modifying an S T Snowmobile and prior to racing the engine should be run
42. d in Modifying 440 S T from Stock to Modified Stock preceding 2 Inlet Port Enlarge cylinder inlet port Figure 1 as outlined in Modifying 440 S T from Stock to Modified Stock preceding B Piston Modify piston Figure 2 as outlined in Modifying 440 S T from Stock to Modified Stock preceding Ii SD NW X X BR Machine 0 065 from Face of Cylinder Head X X x w X X X X X5 x X OX X E e 7 CX X X X S XS Naaman enm wes n X Ww NITE E Lei SS X Remove Sharp Re Cut Squish er Edge from Area at 20 Sg ui sh Area B n _ Shape of Stock Cylinder Head pus __ Shape of Modified Figure 4 m cc ae Cylinder Head 440 S T Super Ee Modified Exhaust Figure 3 440 S T Super Modified Cylinder Head Header Pipe C Cylinder Head 1 Machine 0 065 1 65mm from face of cylinder head Figure 3 2 Recut cylinder head squish area at 20 and out to original diameter 2 657 64 49mm Figure 3 3 Remove all sharp edges from edge of squish area Figure 3 4 Volume of modified cylinder head measured on flat plate should be 23 8cc D Ignition Timing Retard ignition timing full advance from 0 100 2 54mm BTDC to 0 080 2 03mm BTDC Page 4 Snowmobile Tipster No 75 7 EXHAUST SYSTEM A Exhaust Header Pipe C
43. ding Chamfer Weight Piston Assembly Complete 30 4 0 7 mm 30 0 0 7mm Overall Height of Piston thru Center 70 5 0 8mm 713 0 8mm 68 7 0 8mm 67 15 0 8mm 0 0 8856 62 0 0 86 Crankease Face to Center of 70 0 05mm Crankshaft DBA Level aS Head Pipe Length D 9 OF 1 563 0 025 1 Piston TDC 2 Y Pipe Manifold with Single Expansion Chamber and Muffler Assembly 8 Twin Expansion Chambers Discharging into Single Muffler OVER x Ring Thickness 2 515 8 611 395 Ring Width s 3 0 2 7mm Height of Piston Exhaust Sidd 65040877 680208 680208 0 6 A Height of Piston Intake Side 63 0 0 8mm 65 0 70 60 0 0 8mm RingType L andRectangular L and Rectangular L Keystone J 72 5 1 995mm 212mm 70 0 0 5mm 70 0 0 40 0 192 1 563 0 025 3 1 5 0 192 0 0 NA Not Applicable 335 10 198 0 10 0g 240 0 10 0g 1976 440 S T Kohler 440 RLC E 435B8cc N A Liquid 98 mm 60 0mm Thunderbolt CD 07mm Chrome Plated Alum 96 0 1 0mm 46 5 1 32 1 1 0 15 2 42 0 71 31 04 1 2mm 30 5 0 7 42 0 0 5mm 35 0 0 5mm 135 1 0mm 34 0 0 3mm 335 0 7560 308 0 10 09 707 08mm 64 0 0 8mm 2 Keystone 2515mm i 3 0mm 70 0 7 x NOTE See Bottom of Page 2 for Metric U S
44. e El ah amm C tin u nc WA E gt Aa w AN a optem Tere Tu 4 SE P 3 KI Et Hien PET dl a d H SI eer 1 1 Wi P vy TR Mo 7 Y 2 ai el fc dad d BET KEE E Sno Twister Hi Performance Tipster NOTICE Sno Twister Hi Performance Tipsters are in number ical order starting with 75 1 IF the first copy you receive is exampte 75 3 and you desire previous Tipster issues 75 1 and 75 2 advise Mercury Marine Publications Dept P O Box 1108 Fond du No 75 5 II 22 14 Lac WI 54935 and give the first number that you received 1974 75 Race Proven Set Up Tips It s official On the weekend of November 2nd amp 3rd 1974 in Alaska Mercury Sno Twister Snowmobiles kicked off the 1974 75 snowmobile racing season with resounding victories in Stock II and Stock III classes Here are some set up tips that helped pull it off IMPORTANT These set up tips and specifications are intended for use under race conditions ONLY ENGINE and CARBURET ION 1 Check ignition timing 100 005 BTDC at 3000 RPM Make sure that idle RPM is set low enough to permit drive clutch to reset disengage from belt Idle RPM too high causes belt drag resulting in a slower start off the line 3 Set the low speed mixture needles air pilot screws on both the 340 S T and 440 S T at 2 turns open from seat 4 Set carburetor Jet needles a
45. e adjusted for firm or soft ride depending upon rider preference Best weight transfer requires a soft setting at rear refer to Owner s Manual es Track slide suspension alignment Align track first to slides then to chassis tunnel NOTE Because the front control arm always is in compression it may be necessary to rework the suspension mounting holes slightly and adjust alignment with the suspension bolts loose in order to achieve perfect alignment of the slider suspension inside the chassis tunnel Traction devices Three types of studs are available from Mercury Marine for various types of racing surfaces and conditions D 68441 Merc Stud 22 Pcs Per Package D 71925 Merc Scat Stud 22 Pcs Per Package D 71926 Merc Carbide Stud 22 Pcs Per Package Placement and pattern are strictly rider preference depending upon rider style and racing surface The rivet in the outside ends of each track bar can be removed if absolutely necessary to place a stud Track lubrication Lubrication of the track can be beneficial by reducing drag between track and sides of tunnel and between drive sprockets and track STP lubricant works well Skis carbide wear skegs Carbide wear skegs are a MUST for stock racing and are available from Mercury Marine D 68440 1 Carbide Skeg Pair 10 Carbide Inserts D 71334 Carbide Skeg Pair 6 Carbide Inserts Badly chipped bent or broken carbide skegs should be replaced immediately Placemen
46. e the 4 lockwashers on the 4 NEW retaining screws will result in damage to the rotor and could alter ignition timing a Place MACHINED side of balancer against lower pulley toward engine b Install lockwashers retained in Step 2 on 4 NEW screws apply Loctite Type A C 92 32609 to threads of screws and reinstall starter rewind cup with screws 4 Reinstall rewind starter assembly OVER B DRIVE CLUTCH WEIGHTS ALL 1976 Model 340 S T Attach Bulletin Reference Sticker on Section 2C Index Page of Your Snowmobile Service Manual ALL 1976 Model 340 S T Snowmobiles MUST BE equipped with 135 weights D 71737 in the drive clutch assembly 6 weights per clutch Some 340 S T Snowmobiles CHASSIS Serial No 4405867 and Below were shipped from the factory with 106 weights in the drive clutch and these ARE NOT LEGAL for Stock II class racing To remedy IMMEDIATELY notify owners of 1976 Model 340 S T Snowmobiles to check the drive clutch for correct 135 weights INSPECTION PROCEDURE Part No stamped into perimeter of drive clutch cover as follows INCORRECT XXXX 088 CORRECT XXXX4888 or XXXX 989 088 088 2 OR visual inspection of the Part No on the weights thru vent holes in drive clutch cover as follows INCORRECT XXXX 106 Color Red CORRECT XXXX 135 Color Black IMPORTANT 11 the weights are incorrect and must be replaced REMOVE the drive clutch assembly from the engine before attempting clutch disas
47. ecessary to tape off a portion of the radiator to maintain the recommended engine operating temperature above 110 F 430 C MINIMUM Frequently check and tighten all hose clamps CARBURETORS 440 S T Engine idle 3000 RPM Calibration No change from standard settings 340 S T Engine idle 3000 RPM Calibration No change from standard settings 250 S T Engine idle 3000 RPM Calibration CHANGE jet needle E rings from 2nd groove from top to 4th groove from top TORQUE SPECIFICATIONS Torque Specs 250S T 340 S T amp 440 S T Cylinder BRIG sure Ahk gre dkna da B 185 in 225 in Ibs Crankcase halves only 155 in Ibs 155 in Ibs King 2 ew EE eae ro roro ES 225 in Ibs 225 in Ibs ROTO HUE La CE hae ee vv g 90 ft Ibs x 90 ft Ibs Screws to water pump cover 2 0e8 95 in 95 in Ibs Retractable starter 85 in Ibs 85 in Ibs Drain plug BENER amp eee wt ze GK 95 in Ibs 95 in Ibs Exhaust Hange CECE a na PG A 85 in Ibs 85 in Ibs Spark plU c o MNA S Eos m CD 18 18 ft 1 in Ib 1 15kg cm 1 ft Ib 14mkg THROTTLE CABLES Occasionally lubricate throttle cable core wires with WD4O or LPS lubricant 1 Lubricate from ends of cables around core wires and or 2 Drill a 1 16 1 6mm hole in top end of cable junction block and lubricate through the hole CLUTCHING
48. enterlines of track drive lugs as shown 11 pcs required Track Bar Rivet Drive Lug Centerline Type 1 Stud Mount Standard original equip ment mounting Torque to 8 10 ft Ibs 1 1 1 4mkg DO NOT attempt to draw head of bolt flush with track fabric Type 2 Alternate Mount Use 74 28 pan head bolt a 5 ID washer with a large OD under bolt head and standard locknut Torque to 8 10 ft Ibs NOTE Drawing the bolt head or washer deeply into the track usually will result in premature loosening of stud and or tearing of track fabric Optional Spacer 340 S T KEY X Merc Carbide Stud Part No D 71926 22 pcs in pkg Super Stud Z Merc Scat Stud Part No D 71925 22 pcs in pkg Kangaroo 1 x 5 8 bite Carbide Stud on every bar alternating from side to side 44 pcs required Scat Stud with spacer underneath to achieve 3 8 9 5mm maximum height allowed Attach to track not on bar alternately after every 4th track bar on centerlines of track drive lugs as shown 11 pcs required Track Bar Rivet Drive Lug Centerline Type 1 Stud Mount Standard original equip ment mounting Torque to 8 10 ft Ibs 1 1 1 4mkg DO NOT attempt to draw head of bolt flush with track fabric Tupe 2 Alternate Mount Use 74 28 pan head bolt a 14 ID washer with a large OD under bolt head and standard locknut Torque to 8 10 ft Ibs NOTE Dr
49. er issues 75 1 and 75 2 advise Mercury Marine Publications Dept P O Box 1108 Fond da No 75 8 12 6 74 Lac Wi 54935 and give the first number that you received TRACK STUD INSTALLATION 1975 Models 340 S T 440 S T and 440 T T Chassis Serial No 4205000 and Above On some snowmobiles wear strips D 70727 in the chassis tunnel will require repositioning if installation of track studs is desired Make certain that the FRONT END of both wear strips extend 4 10 16cm forward of FRONT wear strip attaching hole in chassis Failure to observe this dimension exactly may result in damage to the chassis tunnel with track studs installed If wear strips are not correctly positioned reposition as follows 1 Remove seat cushion fuel tank and slide suspension 2 Drill out 14 rivets which attach wear strips to chassis and remove wear strips 3 Reposition each wear strip so that the front end extends 4 forward of front wear strip attaching hole in chassis Using wear strip as a guide drill 13 64 5b 16mm holes thru chassis 7 for each wear strip 4 Install fuel tank and seat cushion Attach wear strips with 14 rivets C 17 7 1790 6 Install slide suspension and readjust track tension and alignment e SCH Me KA 7 P bep nme o k eee 1 Im 00 Pat dr honey TR st 1 i44 VISTA TS aeq 1 954 115 133 i es M y 0
50. est prior to racing TETHER SWITCH Disconnect on off switch wire from 3 stud of termina block to prevent accidentally stopping the engine Attach a paper clip to the tether switch cord and hook the clip on the throttle cable so that the clip must be pulled free before the tether is disconnected Check the tether switch operation Moisture will cause the points to freeze resulting in a switch malfunction Gasoline de icer will eliminate the moisture COWL The aluminum hinge rivets should be replaced with large head steel rivets or bolts The headlight should be removed or taped and the screws secured with silicone sealer IMPORTANT NOTE U S S A has ruled that we cannot use the boggie wheel kits for racing Important Info about Snowmobile Registration and no Twister Hi Performance Tipster Mailing List Mercury Marine is introducing another FREE customer benefit Owner direct mailing of the new Sno Twister Hi Performance Tipster aimed primarily for racing machines To get the project in gear the following IMPORTANT Tipster mailing list directive will be included in the Snowmobile Information envelope shipped with all Mercury Snowmobiles manufactured after Sept 1 1974 MR DEALER Mercury Marine has made an important change to Snowmobile Registration Cards We ve added RACINGL Je the Primary Use section of the card We ve done this in response to many requests from owners primarily use their snowrnob
51. haust Pipes B Exhaust Pipe Center Sections 1 Cut 0 50 12 70mm from center section at widest part of each exhaust pipe Figure 2 2 Before re welding exhaust pipes position pipes in snowmobile and rotate sections to obtain best fit 3 Weld sections of exhaust pipes together Be sure that welds are smooth and do not restrict exhaust C Exhaust Pipe Stingers 1 Cut production stinger from each exhaust pipe NOTE Converging cone of exhaust pipes may have to be cut back slightly so that inside diameter ID of cones is enlarged to 1 00 25 40mm same ID as replacement stinger 2 Weld modified stingers 1 00 ID x 0 040 thick a x 17 00 lon 1 02mm x 43 18cm Figure 2 to converging cones Be sure that welds are smooth and do not restrict exhaust CARBURETION 1 Remove carburetor air intake box from snowmobile Remove large air funnel from each carburetor NOTE When removing parts muffler air intake box etc from snowmobile keep in mind that you are making the machine lighter A certain amount of weight may have to be retained to meet minimum weight limit 3 Check synchronization of carburetor throttle valves and readjust as necessary CAUTION When in doubt about a carburetor adjustment ALWAYS select a richer setting Carburetors which are adjusted too lean will cause severe internal engine damage 4 Check carburetor adjustments idle speed low speed mixture jet needles an
52. he control arm Reinforce rear suspension control arm as follows A If track guide has NOT BROKEN loose from control arm securely weld a steel strap 100 125 thick x 50 wide to track guide and control arm as shown in Figure 1 B If track guide HAS BROKEN loose from control arm replace quide with a piece of steel tube 1 90 2 00 diameter x 50 wide Flatten tube to a height of 1 62 and weld securely to control arm as shown in Figure 2 Track NE 100 125 Thick Steel Strap 50 Wide Vyeld Rear Bes Control Arm Rear Suspension SCALE 1 1 M e SCALE 1 Figure 1 Reinforcing Rear Gusp risior Control Figure 2 Repairing Rear Suspension Control Arm Arm B i y 1 gt gr 3 er ag a A A aw eet me oum Mi VU OE 71 oen Ar e Y ND m Ku Kr Kaes T An 7 ft E T e GEN 7 LUST 0 T Li Sno Twister Hi Performance Tipster NOTICE Sno Twister Hi Performance Tipsters for 1976 are in numerical order starting with 76 1 If the first copy you receive is example 76 3 and you desire previous Tipster issues 76 1and 76 2 advise Mercury Marine Publications Dept P O Box 1108 No 76 8 1 29 76 Fond du Lac WI 54935 and give the first number that you received 1976 MODELS 250 S T 340 S T and 440
53. iles for racing who wish to receive from the factory owner direct mail of latest information in Sno Twister Hi Performance Tipster bulletins on racing To compile such a customer mailing list via direct computer mailing it is ESSENTIAL that 1 you fill out all registration cards 2 you ascertain from the owner the primary use intended and mark the registration card accordingly and 3 you promptly mail all cards to the factory We re sure that every racing owner will want to take advantage of this FREE direct mail service Only you can get him on the racing Tipster list If he races check RACING C 90 7 1050 5 74 We ll also advise owners in their Operation and Maintenance manual that if racing is intended it should be properly checked on the new machine s Registration Card under RACING a so that the customer will be mailed the Tipster bulletin This Tipster sheet will be used exclusively to notify owners of high performance information and time saving tips IMPORTANT The service is intended strictly as an owner benefit Dealers still will receive an identical mailing at the same time em e RM r NOTICE Sno Twister Hi Performance Tipsters are in numerical order starting with 75 1 If the first copy you receive is example 75 3 and you desire previous Tipster issues 75 1 and 75 2 i advise Mercury Marine Publications Dept P
54. in at part throttle 50 to 75 power for one hour Operate engine at 110 F to 1709F coolant temperature for Break In and all operation thereafter Modifying 340 S T from Stock to Super Modified A limited number of Super Mod Kits are available thru Mercury Marine To obtain ordering information on these kits contact Mercury Marine Hi Performance Products Department 20 Wisconsin Street Oshkosh Wisconsin 54901 Attention Snowmobile Division Telephone 414 231 9180 Sno Twister Hi Performance Tipster NOTICE Sno Twister Hi Performance Tipsters for 1976 are in numerical order starting with 76 1 If the first copy you receive is A EH SNO TWISTER example 76 3 and you desire previous Tipster issues 76 1 and 76 2 advise Mercury Marine Publications Dept P O Box 1108 A PREF Fond du Lac WI 54935 and give the first number that you received No 6 D 12 I 75 440 S T MODIFICATION INSTRUCTIONS IMPORTANT Modification of exhaust system and or engine VOIDS your WARRANTY Modification instructions are intended solely for race applications CAUTION Modify engine exhaust system and carburetion EXACTLY as instructed following ANY DEVIATION from SPECIFIED DIMENSIONS or MODIFICATION of PARTS NOT MENTIONED WILL DECREASE PERFORMANCE and could result in severe engine damage Modifying 440 S T from Stock to Modified Stock
55. ings Make certain that system is mounted securely Drive sheave clutch disassemble and clean Check fiber bushings in movable and fixed sheaves for wear and or binding Check all moving parts for wear and restricted movement Make sure that ramps are properly seated in movable face Engagement RPM can be raised by adding spacers on spring or lowered by removing them No more than four 4 spacers are allowed When reassembling drive sheave be sure to match alignment mark on movable sheave with mark on sheave cover and take care not to bind fiber bushing no lubrication is necessary Driven sheave Disassemble and clean Check condition of torque bracket wear plates Replace if necessary Reassemble and lightly lubricate shaft and wear plates Adjust return spring preload as required approximately 2 ramps to attain maximum recommended RPM at wide open throttle 8250 RPM refer to Owner s Manual Torque converter alignment Check and adjust alignment parallel and offset distance between sheaves Inspect drive belt for wear distortion burn spots and cracking Check drive belt tension If in doubt about condition of belt replace it refer to Owner s Manual Drive chain Drain and refill chaincase with 3 oz 3 1 imp oz of automatic transmission fluid ATF Check and adjust chain tension to specifications Suspension adjustments Understeer and oversteer can be varied by changing spring tension on front cross shaft Rear shocks can b
56. ive clutch cover works best with the aid of an arbor press Credit for the weights and 0 5 hrs labor per snowmobile will be issued upon receipt of a completed warranty claim One claim listing individual CHASSIS Serial Nos may be used to cover service to all snowmobiles D 71717 Weight 2106 6 per Clutch Required D LOWER COWL and SNOW FLAP FASTENERS ALL 1976 Model 250 340 440 Sno Twister Snowmobiles Attach Bulletin Reference Sticker on Section 21 Index Page of Your Snowmobile Service Manual LOWER COWL To be sure that the lower cowl remains securely fastened to the front crossmember we recommend that the 6 aluminum rivets which secure the cowl to the front crossmember silver colored 5 8 diameter head 3 located inside lower cowl in a line on each side of crossmember be replaced with STEEL rivets Mercury Part No C 17 76047 or an equivalent steel rivet 3 16 4 8mm diameter shank x 5 8 15 9mm diameter head with 3 8 9 5mm to 4 12 7mm grip range SNOW FLAP Check the rivets which secure the snow flap and mounting strip to the chassis To prevent the rivet from pulling out thru the snow flap make sure that the clinch end of the rivet inside the tunnel has a backing washer on each rivet Mercury Part No C 12 21273 or an equivalent washer 13 64 5 16mm LD x 4 12 7mm O D x 1 16 1 59mm thick If the rivets are not equipped with these backing washers remove and install new rivets C 1
57. k to Achieve 4000 RPM Max NOTICE Sno Twister Hi Performance Tipsters are in numerical order starting with 75 1 If the first copy you receive is example 75 3 and you desire previous Tipster issues 75 1 and 75 2 advise Mercury Marine Publications Dept P O Box 1108 Fond du Lac WI 54935 and give the first number that you received Driven Shaft Pillow Block 1975 340 S T 440 S T and 440 T T Models We have received a few reports that the driven shaft pillow block D 71007 has developed a small crack as shown in Figure 1 because of the torque load and stress to which the block is subjected Thus far complete breakage has not occurred At this time and only as a temporary measure we recommend construction and installation of a support brace as shown in Figure 2 to reinforce the block A new stronger pillow block with a support brace is in process and will be available soon for no charge replacement As soon as parts are available details will follow in a later bulletin Cracked A Pillow X y Block Figure 1 Cracked Pillow ooo08 Block P Support Brace 4d Aluminum 14 Long Figure 2 Support Brace 7 MI Installed 4 1 7 09009 ay T 2 ae r AD 1 T SE Ts o V NO M d jf sa 3 i 5 1 qu X io 9 VER GI D e H dee Kat 1 L vi 1 1 de Ge M Wer SC WE Erd
58. lding exhaust pipes position pipes in snowmobile and rotate sections to obtain best fit 3 Weld sections of exhaust pipes together Be sure that welds are smooth and do not restrict exhaust C Exhaust Pipe Stingers Cut production stinger from each exhaust pipe NOTE Converging cone of exhaust pipes may have to be cut back slightly so that inside diameter ID of cones are enlarged to 1 00 25 40mm same ID as replacement stinger 2 Weld modified stingers 1 00 ID x 0 040 thick approximately x 17 00 long 25 40mm x 1 02mm x 43 18cm Figure 2 to converging cones Be sure that welds are smooth and do not restrict exhaust CARBURETION 1 Remove carburetor air intake box from snowmobile 2 Remove large air funnel from each carhuretor NOTE When removing parts muffler air intake box etc from snowmobile keep in mind that vou are making the machine lighter A certain amount of weight may have to be retained to meet minimum weight limit 3 Check synchronization of carburetor throttle valves and readjust as necessary CAUTION When in doubt about a carburetor adjustment ALWAYS select a richer will cause severe internal engine setting Carburetors which are adjusted too lean damage 4 Check carburetor adjustments idle speed low speed mixture jet needles and fixed high speed jets Adjust high speed mixture replace fixed high speed jets to achieve normal coloration of spark plugs
59. nition timing to 16 09 BTDC 3000 RPM IMPORTANT Ignition timing will retard slightly as engine RPM increases a normal characteristic of this ignition system For this reason the timing specification of 169 is applicable ONLY at 3000 RPM and is equivalent to 139 BTDC 9250 RPM EXHAUST SYSTEM NOTE When removing parts muffler air intake box etc from snowmobile keep in mind that you are making the machine lighter A certain amount of weight may have to be retained to meet weight limit Replace stock exhaust system with modified exhaust pipes available thru Mercury Marine To obtain ordering information on modified pipes contact Mercury Marine Hi Performance Products Department 20 Wisconsin Street Oshkosh Wisconsin 54901 Attention Snowmobile Division Telephone 414 231 9180 CARBURETION 1 Remove carburetor air intake box from snowmobile 2 Remove large air funnel from each carburetor NOTE When removing parts muffler air intake box etc from snowmobile keep in mind that vou are making the machine lighter A certain amount of weight may have to be retained to meet minimum weight limit 3 Check synchronization of carburetor throttle valves and readjust as necessary CAUTION When in doubt about a carburetor adjustment ALWAYS select a richer setting Carburetors which are adjusted too lean will cause severe internal engine damage 4 Check carburetor adjustments idle speed lo
60. ons E SNO TWISTEH No 75 7 11 22 74 CAUTION Modify engine exhaust system and carburetion EXACTLY as instructed following ANY DEVIATION from SPECIFIED DIMENSIONS or MODIFICATION of PARTS NOT MENTIONED WILL DECREASE PERFORMANCE and could result in severe engine damage Modifying 440 S T from Stock to Modified Stock ENGINE A Cylinder 1 Exhaust Port Enlarge cylinder exhaust port as follows a Raise top edge of exhaust port to a point 1 120 28 45mm below top surface of cylinder Figure 1 DO NOT change bottom edge of exhaust port b increase chordal width of exhaust port to 1 690 42 93mm Figure 1 NOTE Chordal width Figure 1 is straight line distance between side edges of port not following curvature of cylinder wall c Enlarge radius of 4 exhaust port corners to 0 20 5 08mm Figure 1 d After grinding exhaust port chamfer all sharp edges Raise Exhaust Port Lower Inlet Port to 3 850 below to 1 120 below Top Top Surface of Cylinder Surface of Cylinder Raise Inlet Port to 2 470 below Enlarge Radius Top Surface of Cylinder of 2 Top Inlet Port Corners to 0 20 Entarge Radius of 4 Exhaust Port Corners to 0 20 Enlarge Radius of et ae 2 Bottom Inlet Port Increase vx E o Corners to 0 75 Inlet Port to 1 770 1 vig V 1 Pad I Increase Chordal Width of x LL UN Exhaust Port
61. or Break In and all operation thereafter Modifying 440 S T from Stock to Super Modified A limited number of Super Mod Kits are available thru Mercury Marine To obtain ordering information for these kits contact Mercury Marine Hi Performance Products Department 20 Wisconsin Street Oshkosh Wisconsin 54901 Attention Snowmobile Division Telephone 414 231 9180 NAT 9 TM MM i 1 7 HX nme PER d Lr A LX Ae no vum 1 1 y EN ee T 5 1 E gt UT ma EL Alen ns 3 5 UN 2 T 7 1 a ei AI r E y pyy WS a DONT VC Ze be 7 na es rare Om t A T ii 1 4 Sno Twister Hi Performance Tipster NOTICE Sno Twister Hi FE tan Tipsters for 1976 are in numerical order starting with 76 1 If the first copy you receive is example 76 3 and you desire previous Tipster issues 76 1 and 76 2 advise Mercury Marine Publications Dept P O Box 1108 No 76 7 1 2 30 75 Fond du Lac WI 54935 and give the first number that you received 1976 MODELS 250 S T 340 S T and 440 S T REAR SUSPENSION CONTROL ARM Mercury Marine has received a few reports of the rear suspension control arm D 74492A 1 failing on 1976 Model Sno Twisters The failure is occuring where track quide is welded to t
62. ormula 50D 81A TC W Rated IMPORTANT Some 1976 S T Operation and Maintenance Manuals C 90 74530 recommended Quicksilver Snowmobile Oil Quicksilver Formula 30D and BIA TC W Oils all prediluted at a 20 1 ratio Use of these prediluted oils ONLY at a 16 1 ratio are permissible CHANGE any of these Manuals to the above recommendation 16 1 ratio APT os e Nn 72072 j YQ TRIS SER 1 3 s 1 KZ r m oi P TuS i E d KR OT oe am a a YS E Ms um rmm Wie RW ete d 1 el Eu CERT i nm yai di Dr v ihe it CN y A E A Ge d S lt ruwa E x i Twin vs 0 5 J y Le 7 2 Le d 0 ym 3 E i 0 Veep TT A E by EP SY SERVICE STE FEE a s BU LLETIN SNOWMOBILES TO Balancer Installation 1976 Model 340 S T and 440 S T Snowmobiles Drive Clutch Weights All 1976 Model 340 S T Drive Clutch Weights All 1976 Model 440 S T Lower Cow and Snow Flap Fasteners All 1976 Model 250 340 440 Sno Twisters Place in Your Service Bulletin Binder CES A BALANCER INSTALLATION 1976 Model 340 S T and 440 5 Snowmobiles Attach Bulletin Reference Sticker on Section 2C Index Page of Your Snowmobile Service Manual For ALL 1976 Model 340 S T CHASSIS Serial No 4495560 and Above For ONLY 1976 Model 440 S T CHASSI
63. p 041 5 05 341 5 to Bottom of Intake Port ES 5 Ser Overall Length of Cylinder 109 0 0 01 1080 5 z P gt HSC 109 0 1 2 98 342 11595 5 115 95 5 1462 Reed Valve Boost 53 0B HA 34 75 1 0 Heed Valve 92 00 Parave NOA zey 1oquunu 315414 eu AIB pue IM 981 np puoJj AOL xog O d 1dag suoneangng SULE Z S pue L GZ senssi 191sdi snoiaaad auisop NOA pue 6 ajdwexa si amaJa MOA doo 15414 au JI utr Buigueys ep goraeuin u ui omg o2ueuno pio d IH 191SIW Lou 391 LON 0 3800 29 5415 29 0415 4 Depth Top of Cylinder 1 33 5 4 6 34 434 4 6 37 5 1 0 37 5 10 39 11 to Top of Exhaust Port 3 3s P r m l Depth Top of Cylinder 46 2541 5 46 2541 5 47 8 6 1 2 438 2 51 541 0 151 5 1 0 50 80 _to Top of Transfer Port m ROS OS E e Dee ZE E 7 uS cuum 330415 33 0 1 5 35 0 1 0 P 5 Renate 1 Width of Tune Parts 820114 ES 13 0 1 0 127410 0 85 042 0 85 0420 5 Width of Intake Ports or 1 45 0 1 5 43 0415 48 0 1 0 37 0 1 0 Reed Valve Reed Valve Reed Valve Width of Exhaust Ports 400 370 1 5 43 16 424475 37 0 75 0 0 Height of Transfer Ports 14 0 1 0 14 0 1 0 13 7 1 0 10 13510 13 5 1 0 Height of
64. s follows 340 S T E ring in 2nd notch from top 440 S T E ring in 1st top notch 5 Use the chart and graph in the Owners Operation and Maintenance Manual as a guide to determine approximate setting of high speed mixture needles However POSITIVELY determine final setting by reading spark plug color after making a few 100 yd WOT runs refer to Owners Manual for procedure TORQUE CONVERTER 1 Set driven sheave spring preload at 2 full cams 30 32 Ibs 13 6 14 5kg Check for 8250 RPM at WOT and readjust if necessary NOTE To assist future adjustments and or repairs remove burrs from torque bracket ID to achieve a slip fit on the steel shaft of the fixed sheave A light film of grease on the shaft also helps 2 Clean and inspect drive clutch as outlined in Owners Manual 3 Check and adjust drive belt tension as outlined in Owners Manual 4 Check clutch engagement RPM and adjust if necessary IMPORTANT Use a dependable and accurate service tachometer to check RPM Don t rely strictly on your snowmobile tachometer USSA rules specify 4000 RPM maximum engage ment TRACK SUSPENSION 1 Adjust track tension and alignment as outlined in Owners Manual 2 Lubricate drive sprockets and both edges of track for smoother running with less drag STP works well 3 For best results of weight transfer set spring preload on rear shocks soft and set tension on front suspension springs as test results on a particular tr
65. sembly Removal and or installation of the drive clutch cover works best with the aid of an arbor press Credit for the weights and 0 5 hrs labor per snowmobile will be issued upon receipt of a completed warranty claim One claim listing individual CHASSIS Serial Nos may be used to cover service to all snowmobiles D 71737 Weight 135 6 per Clutch Required C DRIVE CLUTCH WEIGHTS ALL 1976 Model 440 S T Attach Bulletin Reference Sticker on Section 2C Index Page of Your Snowmobile Service Manual ALL 1976 Model 440 S T Snowmobiles MUST BE equipped with 106 weights D 71717 in the drive clutch assembly 6 weights per clutch Some 440 S T Snowmohiles CHASSIS Serial No 4349543 and Below were shipped from the factory with 123 weights in tbe drive clutch and these ARE NOT LEGAL for Stock III class racing To remedy IMMEDIATELY notify owners of 1976 Model 440 S T Snowmohiles to check the drive clutch for correct 106 weights INSPECTION PROCEDURE 1 Part No stamped into perimeter of drive clutch cover as follows INCORRECT XXXX 089 CORRECT XXXX 889 089 2 OR visual inspection of the Part No on the weights thru vent holes in drive clutch cover as follows INCORRECT XXXX 123 Color Yellow CORRECT XXXX 106 Color Red IMPORTANT H the weights are incorrect and must be replaced REMOVE the drive clutch assembly from the engine before attempting clutch disassembly Removal and or installation of the dr
66. sis Length 88 00 250 88 33 500 250 33 500 33 500 250 39 250 250 89 250 250 39 250 250 406x056 4 06 4 06 06 3930424 A 35 00 125 __ 35 007 125 Material Rubber Grovser Rubber Grouser W 15 007 125 15 00 125 15 00 125 1035 EE 30200 pem g 5 Overall Vehicle Width Ski Width Center Distance between Skis Track Drive Sprocket Teeth 12 idler Diameter 7 625 7 625 LEET os ZO Standard Drive Sprocket 14 15 No of Teeth Standard Driven Sprocket 34 15 l 7 No of Teeth v4 H Ontional Drive Sprackets 12 13 15 18 17 18 12 13 14 16 17 1B 12 13 14 15 17 18 No of Teeth Optional Driven Sprockets No of Teeth Drive Chain Rows WEIGHT Overall Less Gas 2 Ir a 31 10 SOE TOTS METRIC U S CONVERSION 1mm millimeter 0 0394 inch 1 25 4mm 1 gram 0 0402 1cc cubic centimeter 0 06 cu in 1 Ib pound 0 4536kg kilogram Sno Twister Hi Performance Tipster NOTICE Sno Twister Hi Performance Tipsters for 1976 are in numerical order starting with 76 1 If the first copy you receive is example 76 3 and you desire previous Tipster issues 76 1 and 76 2 advise Mercury Marine Publications Dept P O Box 1108 No 76 2 1 1 26 75 Fond du Lac WI 54935
67. spark plugs CAUTION When in doubt about high speed mixture adjustment ALWAYS select a richer setting Carburetors which are adjusted too lean will cause severe internal engine damage DRIVE SYSTEM A Maximum Engine RPM A modified stock 440 S T will deliver maximum power when operated at 8 500 to 8 750 RPM Modify and adjust torque converter to increase full throttle engine RPM to this speed B Drive Sheave Clutch Install Drive Sheave Modification Kit D 71711A1 Modify profile of drive sheave ramps to attain correct full throttle engine RPM as recommended in preceding paragraph and desired shift pattern NOTE Clutch modification instructions are supplied with modification kit C Sprockets Snowmobile may require re gearing because of increased horsepower a result of engine modification Installation of another driver sprocket may be desired depending upon operating conditions to change top speed of snowmobile MPH and acceleration Refer to Driver Sprocket Chart following Page 3 Snowmobile Tipster No 75 7 DRIVER SPROCKET CHART Number of Top Speed of Snowmobile MPH Teeth Part Number High MPH D 63573 D 64131 D 63318A1 D 64684 D 68439 D 69757 12 Low MPH A Standard factory installed 440 S T driver sprocket Modifying 440 S T from Stock to Super Modified ENGINE A Cylinder 1 Exhaust Port Enlarge cylinder exhaust port Figure 1 as outline
68. t and length of carbide skegs influence handling to a high degree and again are mostly rider preference Special application At this time the following equipment is available from Mercury Marine for special application i e high elevation cross country racing and modified racing D 1393 5872A1 High Elevation Carburetor Kit 340 S T D 1393 5854A1 High Elevation Carburetor Kit 440 S T D 71712A1 High Elevation Drive Sheave Kit 340 S T and 440 S T D 71711A1 Modified Drive Sheave Kit 340 S T and 440 S T C 58601A1 Bogie Whee Kit 340 S T and 440 S T Driver Sprockets 340 S T and 440 S T Drive Chain 340 S T and 440 S T 7 D 69757 12 12 Tooth 2 D 71483 78 pitch length D 68439 13 Tooth D 64684 14 Tooth 2 78 pitch chain must be used with 16 tooth Tooth sprocket 15 1 0 D 64131 18 Tooth 71 One C 23 69842 spacer must be used with 12 tooth sprocket CONCLUSION The aforementioned steps have touched basically on major aspects of setting up a 1975 Mercury Sno Twister for competition Hard work patience thoroughness and a strong desire to win can and will produce a competitive Sno Twister that will win consistently e 5571 22 EM 0 r i 33 a A 1 1 DS 57 1 1 et 8 00 m TA i a T i i r A 9 x 0 E 09 i 1 US 3 nt 9 dei Ei E H ip 1 A e 1 WP e wa Vide en EH 1 YUQ Gan A ow m
69. uds or claws scattered across the center track band Sz a 1 E i 3 A I 1 di EN i Nis L AM e U 0 Y 2 i D dr KAN 0 Ne 1 Jr _ 1 d Ce 9 a 8 1 r V st An Ch I J ftp d 3 a e Y 7 Ch Ss KZ diis GAS d i T d Ar Ame nag PR Hi gt NE Sno Twister Hi Performance Tipster a NOTICE Sno Twister Hi Performance Tipsters for 1976 are in numerical order starting with 76 1 If the first copy you receive is example 76 3 and you desire previous Tipster issues 76 1 and mies SAO TWISTER 76 2 advise Mercury Marine Publications Dept P O Box 1108 No 76 3 R1 12 1 75 Fond du Lac WI 54935 and give the first number that you received 250 5 1 MODIFICATION INSTRUCTIONS IMPORTANT Modification of exhaust system and or engine VOIDS your WARRANTY Modification instructions are intended solely for race applications CAUTION Modify engine exhaust system and carburetion EXACTLY as instructed following ANY DEVIATION from SPECIFIED DIMENSIONS or MODIFICATION of PARTS NOT MENTIONED WILL DECREASE PERFORMANCE and could result in severe engine damage Modifying 250 S T from Stock to Modified Stock and
70. ure 1 3 Reduce boss at top edge of inlet port to a minimum Figure 1 Boss must be large enough to completely cover piston ring when piston is at BDC bottom dead center 4 After grinding inlet port make a 0 060 1 52mm chamfer to bottom edge of inlet port Figure 1 DO NOT chamfer side edges or top edge of inlet port D Remove sharp edges from inlet port by lightly rounding cylinder bore edges of port with fine emery cloth IMPORTANT DO NOT POLISH transfer passages EXHAUST SYSTEM NOTE When removing parts muffler air intake box etc from snowmobile keep in mind that you are making the machine lighter A certain amount of weight may have to be retained to meet minimum weight limit Remove muffler assembly from snowmobile and modify stock exhaust system as follows A Exhaust Pipe Diverging Cones 1 Cut 0 75 19 05mm from diverging cone of each exhaust pipe directly behind header joint Figure 2 2 Weld header joint to diverging cone of each exhaust pipe Be sure that welds are smooth and do not restrict exhaust 3 Reposition spring hooks on exhaust pipes to give sufficient spring tension Cut 0 75 from Diverging Cone of Each Exhaust Pipe Directly Behind Header Joint and Re weld Ir 1 1 zh T Converging Conas E Cut 0 50 from Rotate for Best Center Section Fit in Snowmobile and Re weld Center Cut 0 50 from r Center Section Figure 2 340 S T Modified Stock Ex
71. ut each header pipe down to 2 0 50 8mm including flange Figure 4 NOTE Re weld spring attaching washers to flange of header pipes B Exhaust Pipe Center Section 1 Cut 1 0 25 4mm from center section of each exhaust pipe Figure 5 Before re welding exhaust pipes position pipes in snowmobile and rotate sections to obtain best fit NOTE Spring hooks will require repositioning on exhaust pipes to give sufficient spring tension Left exhaust pipe PTO side must be heated and CAREFULLY bent to fit around engine rewind housing Bend left exhaust pipe in area of first bend just after header pipe Figure 5 3 Weld sections of exhaust pipes together Be sure that welds are smooth and do not restrict exhaust Bend Left Exhaust Pipe in This Area Bend as Required to Left Exhaust Pipe Fit around Engine Right Exhaust Pipe i eg from Converging Cones c Ge ART 1D Rotate for Best Fit in Snowmobile and Re Weld at Center Sections Y Modified Stingers 7 1 9 from t a Center Section Cut Converging Cones Back Approximately 4 and Weld ID of Cones MUST Be Same as ID of Stingers Figure 5 440 S T Super Modified Exhaust Pipes C Exhaust Pipe Stingers 1 Cut production stinger from each exhaust pipe Cut approximately 72 12 7mm from end of each converging cone so that inside diameter ID of cones is enlarged to 1 1 8 28 58mm same ID as replacement stinger
72. w speed mixture jet needles and fixed high speed jets Adjust high speed mixture replace fixed high speed jets to achieve normal coloration of spark plugs NOTE Use fixed high speed jets which are 1 to 2 jet sizes larger richer than those required for a stock 250 S T DRIVE SYSTEM A Maximum Engine RPM A modified stock and super modified 250 S T will deliver maximum power when operated at 9900 RPM running on to 10 200 RPM Modify and adjust torque converter to increase full throttle engine RPM to this speed B Drive Sheave Clutch Install Drive Sheave Modification Kit D 71711A2 Modify profile of drive sheave ramps to obtain correct full throttle engine RPM as recommended in preceding paragraph and desired shift pattern NOTE Clutch modification instructions are supplied with modification kit C Sprockets Snowmobile may require re gearing because of increased horsepower a result of engine and exhaust modification Installation of another driver sprocket may be desired depending upon operating conditions to change top speed of snowmobile MPH and acceleration Refer to Driver Sprocket Chart following DRIVER SPROCKET CHART Top Speed of Snowmobile MPH No of Teeth High MPH D 6975718 D 69757A17 D 69757A16 D 69757A15 D 69757A 14 m D 69757A13 D 69757A12 agis factory installed 250 S T driver sprocket BREAK IN PROCEDURE After modifying an S T Snowmobile

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