You can adjust the high speed needle by ear quite easily. With the engine running full throttle turn it in a few clicks at a time, wait for the engine to settle into the new adjustment. Eventually you will hit a point where it will begin to slow down, this is to lean. From this point rich-en the mixture a quarter turn or so. What you are seeking is a high speed adjustment that is several hundred RPMs below the maximum RPMsetting. At this point you may have to readjust the low speed needle also.

Additionally do a search for Pinch Test here in the forums for a procedure to use to verify you are not to lean or too rich. What the instructor did can be done if the engine is still too rich. You do indeed want a slightly rich setting as a lean setting will indeed damage your engine. It is possible to ruin an engine with a single excessively lean run.

If you engine is properly adjusted then you need to check your fuel system for leaks.</p>