Would someone please explain the pinch test and how to interpret the results.

Is this test only at an idle?
Does it work for both 4 and 2 strokes

No

Yes

Pinch the line and see if the engine speeds up. If it doesn't, you are as lean on mixture as you should go and maybe you should screw the needle back out a little

You can use it for high speed as well as idle.

You just pinch it momentarily or the engine may go too lean and quit on you.

It works for four Strokes as well as two strokes.

Enjoy

Jim

The pinch test works because excess fuel (if running rich) tends to collect inside the crankcase so it acts like a very small fuel tank. This isn't really desireable

Pinching the line, particularly at idle, stops any fuel from going through the carby which allows any collected fuel to begin to go up into the cylinder. As the fuel gets used up it gets closer and closer to being an ideal mixture so the revs begin to rise then when nearly all the fuel is used the revs begin to drop as it leans out.

That's the theory, in practise what you're looking for is a very slight rise in revs when the line is pinched. This means the mixture is just barely on the rich side of being perfect. The rise in revs should be almost immediate after pinching the line and only last for maybe a second. If it's too lean then the revs will start to drop the moment the line is pinched. It's a bit harder to do at full throttle though because any excess gets used up very quickly.

Thank You w8ye and downunder for sharing your knowledge.

Regards,

Dennis