My 220 is backfiring through the exhaust i put a cobra muffler on it. i thought it was running lean so i richened the mixture but it still backfires when you rev it up and on deceleration. thanks

 

Are you sure you leaned the mixture? Which way did you turn the pilot screw?

Minor backfiring on deceleration is no problem; you might want to run a plug check to see if you need to change the main jet. With only a pipe transplant, I doubt it.

Regardless, a plug reading will tell the tale.

Tree Farmer