Ditto on what Giestware posted. 4 strokes will kick off props if too lean. I've seen some ejected props travel well over 100 feet when kicked off of even smaller 4S. I don't suggest that a beginner use the pinch test on a 4S engine. Instead, use a tach to find maximum RPM and richen needle so you are a few hundred below maximum RPM.

Pinch test is safe for a 2S engine.