[cameron02]

I had a similar problem years back. I had a dodge with a 440 magnum (spec) motor. The custom headers went to some weird places due to the engine being a tight fit. They used to get real hot. The spark plug leads caught fire when running the motor in. There was so much heat that the fuel was vapourising in the lines. It went away at full throttle because there was enough flow to keep the fuel cool but when just crusing it ran like a dog. Took me ages to work out what it was. Anyway, I moved the fuel lines and fixed the problem.