My Bad--I posted the last entry in the wrong thread. After much work and many failed attempts to run the "throttle governed engine" I have reached a conclusion. There were no real flaws in the self governing mechanism. The flaw was that I couldn't get the basic engine to run properly. The new cylinder heads with the sparkplugs moved didn't really help. The ignition cam on this engine mounts onto the crankshaft. The crankshaft rides on bronze bushings that have rapidly worn out, due to the crankshaft not being perfectly true with no runout. The slop in the crankshaft bearing lets the crank move around enough to screw up the gap in the ignition points. I have put the engine up on the shelf, and at a later date I will remake the main crankcase and design it so the crankshaft and camshaft both ride on sealed roller bearings. Sealed ball bearings, surprisingly, will tolerate a bit of run-out in the crankshaft, and are not harmed by this.