We have a 1990 bayou that from time to time runs rough, won't rev up, misses and backfires intermittently. The carb has been gone through by both myself and a shop... The fuel valve needs a rebuild, it leaks when off but allows fuel to flow without issue when pointing to on. This issue seems to go away sometimes then come back at random times. Are there any kill switch disconnects I could check? What would be some good tests?

If anyone rides snowmobiles it seems very similar to the famous TSS issues on arctic cats when they start to fail.

 

Anyone? I would really like to get this ATV running

 

I had similar problems with mine when I bought it (not sure about the backfiring though) and the problem was the vent in my fuel tank cap wasn't working. It would stall out and I'd have to take the cap off to get it to start back up. I put a different cap on it and the problem never came back.
Water in the gas would make that happen too.

 

May try running with air box lid for an few seconds to see if its runs better...if it runs better inspect the air snorkel for an rats nest or dirt dopper nest..restricts the air flow......Get back with us here thanks...