› Forums › Car Problems & Maintenance › Mercury › Why does my 1963 Mercury 390 backfire only at idle?
May 13, 2025 at 7:28 pm
#1393
Michael
I would start by letting it idle and spraying some fluid around the carburetor gasket and the intake gaskets… if it changes the idle, that is more than likely the culprit… try to snug the carb bolts down first.