All's well that ends well.
Thought I'd have another try to get the generator running. Still at the same altitude.
Held the throttle partly closed instead of fully open as the governor linkage wanted, and it fired straight up. Got such a surprise that I let the governor linkage go and it went to full throttle again as it hadn't reached full speed and the engine died again.
Tried again but held the linkage for a bit longer until it reached something close to normal speed and it ran as normal.
Loaded it with the microwave and ran perfectly.
Guess trying to start it with wide open throttle effectively "flooded" it and the fuel air mixture was so rich it couldn't fire.
So they will run at 11,000+ feet, just that they need a bit of help getting started.
