What do you have the ground on the MSD hooked to? That has been one of the biggest problems I have run across. If you turn the rev limiter off does it give you any trouble? I have also had trouble when (with a stock dist.) if you wire it backwards giving timing issues. Are the pick up wires from the box (purple and green) running near plug wires or the coil wiring? On some of the MSD systems there is a purple and green and there is a blus and green. Does yours have both? If so make sure its hooked to the right ones! Ask me how I figured that one out!