I found out why it would go.
The offset key in the crankshaft had sheared and was no longer a key in the crankshaft, just a very full slit and and some scoring.
I got another and fitted it. he flywheel is now TIGHT!!!
The engine runs great, sounds much improved and it definatley has a higher rpm so with a bit of luck the centrifugal clutch will work OK.
I installed my new exhaust and silencer and am just at the stage where I have to put the engine in.
I'll keep you informed.
.>)