Over revving and other issues

[Nick H]

Chris could be on to something here. With the air cleaner removed have a look at the position of the big round disc aka air metering flap.

If the flap has no resistance when you press it down after just switching off the engine then that plunger/piston could be stuck. In your case the plunger would be sticking just at the bottom of its travel. This might make it very difficult to diagnose as the amount of free movement between the leaver and plunger could actually be very small.

But basicly the plunger won’t be pushing down on the leaver attached to the metering flap allowing more fuel and air into the engine than you should have.

Maybe if you give the fuel metering head a light tap with a plastic/rubber mallet when the engine idle is high and see if the idle speed changes?

Be careful if you end up removing the fuel metering head as the plunger can drop out.

Nick H