@mike.....
Took your advice, put on a very old shirt. The flyweights and/or governor sleeve were stuck. It was an easy thing to get unstuck. re-fit the gov linkage and gave it a spin without trying to start.
Crikey ! ! ! Stuck again, and I could see no obvious cause.
With the need for more information, I then removed the camshaft cover (after first removing the gib key, and the flywheel, and the injector pump, etc)
Nothing amiss, the bellcrank was free and not deformed, the governor sleeve was free to slide and rotate, the flyweights were free. WTF?
I held the sleeve while slowly rotating the crank and then found that one of the flyweight fingers became stuck on the sleeve, jamming the whole assembly.
A small, sharp burr on the sleeve face where the bellcrank roller rides is the culprit. It could be remedied with a few passes of a file, Quite easy except that the camshaft has to be removed in order to gain access for smoothing out the burr.
Maybe tomorrow.
Cheers
Hugh