Pinching the fuel line is an effective way of shutting off your engine. As a test, you can tell if you are running lean or rich by how long it takes to shutt off. If you pinch the fuel line and it shuts off quickly, I believe its lean, if it takes too long, then its rich.
actually its the other way around
see the pinch test just makes all the fuel in the carb burn up
so when an engine is lean it burns up less fuel compared to an engine that is rich which burns up the fuel quickly
hope that helps
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