My brother has a 2004 Bayou 250 that backfires out of the carb while idling, it backfires something like once every 10 - 15 seconds. The idle has to be set kind of high or it will die out when it backfires. I've checked for vacuum leaks (no leaks), carb has been thoroughly cleaned, and rebuilt, fresh fuel, put a in-line fuel filter on it. Set the idle mixture screw at 3 turns out, and tried going lean, and richer on the idle mixture. I also put on a new air filter, and a new spark plug gapped at .028". It was doing this before all the work was done to it, but other than that it runs really good with no other problems. I'm out of ideas as to what to try next?

 

only time I've seen backfiring out the carb was from valve problems. Tried adjusting the valves lately?

 

No, haven't tried that yet, Guess I'll check them out.

 

Finally got around to adjusting the valves, they were tight (you could barely feel what lash it had). Set them to factory specs, and it runs a lot better, no popping out the intake, and a little pop out the exhaust every now and then when you let off the throttle. Now you can hear a little clicking from the valves, where you couldn't before.

 

I was bound to get one right eventually