› Forums › Car Problems & Maintenance › Mercury › Why does my 1963 Mercury 390 backfire only at idle?
May 13, 2025 at 7:27 pm
#1389
Scott
If your timing is correct then it’s in the idle mixture. Check for vacuum leaks with carb cleaner. You need to find someone in your area that really knows how to work on carbs, it’s not easy. What’s base timing set to?