Backfiring

[mclldavidson]

I have a mid 90's Yamaha gas, I finally have it going but it does backfire often. My muffler is off, could this have any effect on it?

[Mr. Mike]

My question to you is when is it backfiring? During deceleration, like a pop, pop, pop or when coming to a stop and reapplying some throttle and it lets out one loud bang?

The muffler could have an effect on it

If it's letting out one loud bang than more than likely the butterfly on the throttle linkage isn't closing all the way. Look at the carb and turn the adjustment screw out 1/4 turn at a time and drive it. That should stop it.

If it's popping during deceleration than it could be a lean condition. Are you using the stock air box and breather? Put the muffler back on cause that can cause a lean condition.

Somebody else will weigh in on this as well.

[mclldavidson]

I will drive it today and see exactly when it is backfiring. I do know it is one loud pop and not multiple at the same time. I think part of the muffler is broke, it was off when I bought it and it is the stock air filter. Where is the carb adjustment screw? Is it the only screw visible on the carb?

[Mr. Mike]

It should be the only screw that is visible. It's basically a set screw that would work as an idle screw. In another words the throttle linkage rests on the screw and turning it in would open the butterfly more and turning it out would close the butterfly. Just turn it out a 1/4 turn. If that doesn't help and the butterfly still looks a little open you may need to put a small spring on the linkage to insure that it's closed all the way.