it is likely (particularly where you have NO poping on decel) that your idle set up is way to rich...a little poping on decel is proper on a well tuned vacume slide carb...no poping at all indicates that you are running rich enough to allow for the much higher air flow and no fule flow, caused by a high rev, no throtle, condition, it is probable that it is a carb back fire...but not a sure thing
