I had exactly the same thing about 2 months ago..... Have you lengthened any wires.... I had to, to get it in the plane and it turned out to be a simple answer....... I had lengthened the two (Both Black) glow plug wires and when I soldered in the extra lengths I had crossed the wires over which I didnt think would matter as both were black and are only glow wires after all !. There must be some sort of common negative though because when I swapped them back all worked well. I had also plugged the temp sensor in the wrong way round at the ECU Which didn't help............

This is a lovely engine and I am sure this might be your problem..... Keeping the Glow wires away from the RPM Sensor is also important

Dennis

www.densplanes.co.uk