You’ve got questions. We’ve got answers — Mondays, when the Summit Racing tech department tackles your automotive-related conundrums. This week in our Monday Mailbag, we’re trying to cure a plug fouling condition at idle.
Q: I own a 1971 Dodge Demon with a 400. The 10.5:1 compression engine has a forged crank and “LY” rods, and has a balanced bottom end. The heads are 906 castings port matched to a Weiand Team G intake and 2.5-inch headers. The heads have also had port work done. The cam is a Mopar Performance grind with .509-inch and 292-degree duration at .050-inch lift.
The problem I have is when I let the car idle for 10-15 minutes, the spark plugs get fouled (the motor always runs on the rich side). I thought the problem was with the Holley 0-3310 750 cfm carburetor so I replaced it with another carburetor of the same style. The problem is still there. I changed jets from #72s to #68s, put in a 2.5 power valve, but that didn’t help. When I turn the idle mixture screws in, the engine doesn’t shut off.
A: The classic 0-3310 is not a bad choice for your Demon; however, a 750 cfm double pumper would give you maximum performance. But even the double pumper will not help your plug fouling problem. Here are some things to do to solve that: