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Discussion Starter · #1 ·
need some help finding the problem with my 421 cub motor. The right cylinder is making smoke out of the pipe when riding and the left cylinder has no smoke at all. Bike still runs really strong but not quite as strong as it used to as compared to my buddies 421. just looking for some things to start looking for to find the problem.
 

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Start with simple things like:

Completely cleaning the fuel system (gas tank, screen, lines, remove the carbs, bowls, etc., remove all brass, clean it all good)

Make sure the carbs are sync'd. Check compression in each side. Switch spark plug leads to see if the issue follows from one side to the other. Check your flywheel pickup gap on both nubs, set it to .015 to .018.
Make sure the filters are clean....check your wiring harness for broken/burnt wires, attach new grounds.

Try bypassing/removing the kill switch just to check.
 
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