[Purdy Swoft]

A vacume leak will create a lean condition that can cause popping and backfire . Pot metal carburetors are known for vacume leaks, usually at the flange where the carburetor mounts to the manifold . Over tightening the bolts at the manifold flange can warp the flange on the carb . I would remove the carb and use a straight edge to check the carb flange for warpage . If the float is set just a little too low it will cause sloshing of gas in the bowl of the carb that can result in flooding and stalling when coming to a quick stop . The sloshing will flood the carb and usually cause the engine to stall . The flooded gas will enter the muffler . After the engine warms the muffler can get red hot , especially if the timing is too retarded . The hot muffler will set off the flooded gas in the muffler and cause an embarising loud backfire. .