[marklotus]

My Cobra did not want to rev over 4,000 RPM. It was fine at low RPM but under load at higher RPM's it would sputter and break up. I had the car at a high performance Ford shop and they tried everything...battery, carb, coil, plugs, valve adjustment, valve springs, ignitor and other stuff that I forgot. They tried everything and nothing seemed to work. Eventually they found that someone had tapped into the coil wire for the electric choke. At higher RPM's the voltage wasn't there for what the coil needed to fire properly.
A very simple fix but a difficult to find problem.
I hope this saves someone a lot of frustration.