1990 yamaha big bear 350

[Matt Taylor]

I have a 1990 big bear 350. It just started dying and back firing while being rode. Also tries to die out while riding. If I down shift then shift back up it runs ok for a few minutes. I've read a few things that the fuel could be to lean and needs adjusted. My buddy said timing chain. Any help would be appreciated thank you

[MtBob]

Could be water in the float bowl,or a piece of floater dirt.loosen and remove bowl drain screw,turn on fuel and let some run out,it may wash it out.

[Arby911]

99% chance it’s a fuel delivery problem. 

[Barrysquad]

Thanks out there, I’ve also got a 1990 Big Bear 350 and I’m having the same problem. Sometimes it runs perfect but, then intermittently misses and farts. I don’t think the Big Bear can change timing. It’s all in the Black Box. So I’m going to drain my tank, flush it and clean the petcock. Then change fuel filter and clean float bowl. 👍🏻

[Frank Angerano]

That’s a great way to get after it.  Make sure you clean the rest of the carburetor and not just the float bowl.  Throw a new spark plug in as well. Count the turns you unscrewed the air fuel screw out of the carburetor as well. This way you put it back exactly where you took it out.  Should be about 2-1/4 ish turns.   Good luck. 

[Willie Toombs]

also if you have an aftermarket exhaust it can play havoc on some machines without some fine tuning.