I had similar symptoms that traced to a broken wire going to the coil. The outside of the wire looked fine, but it was broken inside the insulation. Wiggle it right and it would lose power, then it would come back. Took forever to find the problem. I replaced everything but the wire. The my Dad came by, had me fire it up, and started shaking everything under the hood until it acted up. Evidently he had seen it before as well.
