I don't really understand what you've just told me, Paul. Why not try removing the wire link from the throttle butterfly, and controlling the engine with fingers on the butterfly lever? Don't let go of it of course, or it will probably blow the engine. As an alternative, you could rig a piece of stiff wire from the throttle butterfly to a stationary part of the engine (not part of the governor) and try to vary the engine speed by bending the center of that link. The idea is just to see whether the engine runs properly when the whole governor system is eliminated. If it won't run properly with the governor excluded from having any effect, we have an engine problem of a fairly unusual type, and I think you are going to have to go back into the crankcase to re-check the camshaft timing and inspect the decompressor mechanism.

Just to ensure you are as uncertain as I am, I'm pondering what the symptoms would be if the decompressor is stuck in the start position. Some years ago I worked on a couple of veteran cars which had manually-controlled decompressors because at 4.6 litres and with a high compression ratio (they were factory-team racing cars), there was no way you could crank them without decompressors. I even verified that by using a starter motor to rotate the crankhandle without decompressing: it immediately sheared the cross-pin in the front of the crankshaft, where the crankhandle engages. The Hulk himself could not have cranked those engines. So, the point in this story is, when you started the engine in its decompressed state, you had to move quickly to disable the decompressor, or the engine would stop. Meanwhile, it ran absolutely atrociously.

So, if your decompressor is stuck ...

Last edited by grumpy; 17/01/15 06:41 PM. Reason: Add detail