I have a 2003 Yamaha bear tracker that skipped time, I put a new timing chain on, lined everything up, adjusted the valves to spec, and it won’t run right, 1st and 2nd gear is fine but when you go into third it bogs down and jerks, I can lift up the rear and out it threw all the gears and it’s fine, only when it’s on the ground, under a load it will bog down, I put a new intake on, brand new spark plug gapped to spec, cleaned the carb like 5 times, cleaned out the gas tank and fuel petcock, new fuel line and still the same thing, anyone else have any thoughts what I should I do next?

 

Double check the valve timing. Do a compression test, just possible the piston hit a valve and bent it slightly, though bad starting is usually what you get if compression is down. Check the voltage across the battery when running, should not go over 14.5v, this shouldn't affect ignition as the charging circuit has nothing to do with ignition, but from experience, I find it does. Check the float level, but it could be time for a rebuild kit or one of those cheapo carbs. Finally it could be an ignition fault, coil, CDI or stator/pickup coils. If you need to go for substitution, it is going to get expensive.

 

Charging system in fine, I adjusted the intake valve at 0.02-0.04 thousandths and exhaust at 0.04-0.06 thousandths. One it’s warmed up the problem isn’t as bad. I’ve owned it for 2 years but I don’t think the carb was ever rebuilt, I’ll try a compression test. But it starts up nice and easy, runs good until that bog, I have a video of it but idk how to post it