"A four - stroker has a less complex sound than the two-stroke engines discussed in the last section, and that makes them the easiest engines to adjust.  As with any other engine, initially set the high speed needle valve according to the manufacturer's recommendation.  If you purchased a used engine or don't have the instructions, try three turns.  Either setting usually puts the valve somewhere in the usable RPM range.  After starting, open the valve until the engine runs roughly at the rich end of the usable range.  From that setting, closing the valve will be accompanied by a steady increase in speed until the engine slows down or has a loud popping sound distinguishable from the normal tone.  In the latter case, we have preignition.  Both symptoms indicate the valve was closed beyond the usable RPM range.  At that point, richen the valve until the engine smooths, and it will be running near its maximum practical RPM.  You could then refine the setting slightly by using the pinch test.  After successfully performing these tests, it's time for the break-in."