Pinch test:

It's discussed elsewhere, but let me try to restate it.

The pinch test permits you to see if the engine is running too rich or lean.

You are supposed to tune the engine as indicated then while running it at low throttle PINCH off the fuel line leading to the engine.

The engine should speed up and run for 2-3 seconds then die.

If it continues to run longer the engine is too rich.

If it dies quickly without speeding up just a bit, it is too lean.

The pinch test should also be done at high throttle.

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1/3 tank rule.

Engines lean out as the tank empties.

So it is best to test with everything in a "worst case".

e.g. 1/3 of a tank (or less) and then do both the pinch test and the nose up/down test.

You want the plane dying on the ground with any problems so you can fix them, not in the air...