We have a 1999 big bear 350 that has been sitting for 5 years, I have pulled the tank and cleaned carb, changed plugs and still back fires.
Any suggestions?

 

My 96 backfires when its cold.

 

Does it backfire at idle? If so, you can richen the idle screw by turning it counterclockwise 1/4 turn at a time until it quits. Make sure the carburetor is good and clean first though. Sometimes it takes a lot to get them clean.