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. Could the problem be with my ignition? I have an electronic distributor with mechanical advance, the “chrome” ECU, an ACCEL Super Coil, and ACCEL 300+ wires. The car also has a Torqueflite transmission with a 3,000 rpm stall TCI converter and a Cheetah manual valve body. The Demon probably weighs 3,000-3,200 pounds. Is the 0-3310 right for this car?

close up look at cleaning a spark plug electrode tip with fine grit sandpaper

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:

  • Keep idle speed around 880-900 rpm in drive.
  • Check your distributor advance curve. You should have 10-12 degree initial timing with 36-38 degrees total by 2,500 rpm.
  • Keep engine operating temperature around 180 degrees.
  • Switch to an MSD 6AL series ignition and a Blaster 2 coil.

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