Mercury Snowmobiles Discussion Board

Replace the FLOAT NEEDLE & SEAT on the carb...that is causing the overflow & rich condition...

Swap the carbs & see if the problem stays with the carb or the cyl...that will tell you if it's the spark or carburetor. If it moves to other cyl, spark is OK & carb is the problem. www.cdibox.com has CDI boxes for the MERC's with a good warranty

I never knew they said 429 or 436. They were all 67.5mm bore & 60mm stroke (75-4402RS), so regardless of what it said, they are the same displacement & same parts...

Some parts will swap, chaincase & gears, yes, jackshaft...no. The secondary will fit, but the 76 ARCTIC is a better choice. Brakes are the same, drive-shaft is different...

7/16"

Same as the other post...you have a hi-speed stator coil failing BLUE wire to engine should be 76-ohms....yours is probably failing too....common problem & it won't rev over 3000 RPM without backfiring & stalling out...

Measure the hi-speed stator winding...BLUE wire coming out of the engine w/CDI removed. Measure from engine crankcase to BLUE & should be 76-ohms....check COLD & WARM...I bet it's changing! Basically, your Stator is failing....

34RS is the original 36mm carb for the 75 340...should have a #320 main jets. Yes, there is a more reliable CDI available, but no point in changing it if the CDI is still working.

Look for a 12-pole tach...same as on RUPP's from 75, Ski-Roules, Boa-Ski's (any Kohler engine w/Prestolite ignition)

Yes, the original carbs did have adjustable mains on the 75's. Should be 36mm VM36-24 if original, but 38mm's were available from dealers as an upgrade.

It has to be a 1974 Sno-Twister Free-air 400 with that date-code.

It's your stator...common problem, likely the high-speed winding (blue wire). Here's a link to measure the values

http://www.hewtechelectronics.com/image ... WIRING.pdf

It's your low-speed winding yellow wire should be 2.7K, probably much lower. Here is a link for the correct stator resistance values

http://www.hewtechelectronics.com/image ... WIRING.pdf

check the stator values of low-speed winding...yellow wire to engine-ground should be greater than 2600
(2.6K) ohms. Hi-speed winding is around 75-ohms (blue wire) Check cold & warm.

start with 1" dia at 11" length....