High revving engine

[Stuoyb]

Club Parts Service have 928/300 & 930/300 on the shelf

[tubab]

Your very first comment pointed to the problem. Putting your finger across the intake slowed the engine down, so the additional air could only be coming through the intake, any leak further down the line, say at the manifold, and your finger would have much less effect. Even with the throttle slide fully down a very worn slide/carb will give hi revs, think the cable was the problem in your case.