Norm, the problem may not be with your carby, especially if you've tried a few and all are giving you the same symptoms.
Over-revving is generally from a vacuum leak causing it to run super lean and rev it's guts out normally caused by carby a diaphragm that is not sealing correctly but i assume you've checked and double checked that on all of them, or by a dodgy o-ring somewhere. So i propose a couple of other things. 1)Is the pickup off the flywheel clear. Hook a fuel line up to it and see if it's clear when you blow through it. 2)Are both o-rings on the manifold in good order? 3)Starter o-rings? The big one and the small one on the shaft. Finally, the seal on the bottom bearing may be shot which will require a complete tear down of the motor and probably a bit more troule that it's worth.
Cheers, Ted
