I assume you are referring to the Magnums when you say this motor. The Magnums are made of metal. That metal is either really tough under certain conditions or really not tough under those same conditions. High and low end needles make NO difference to that situation. However, richer or leaner settings DO, because a leaner engine runs hotter, creating one of those pesky conditions I was speaking of above. Now, under those conditions a Thunder Tiger is going to hold up longer than a Magnum, and a Magnum is going to bake itself because the metals in it are susceptible to the heat created by the lean running. I've been setting both high and low speed needles for every imaginable kind of engine for 25 years now. My company field tested numerous brands of engines, one of them being Magnums, and each engine has its own idiosynchrasies, likes to be run richer or leaner, uses different types of fuels, and to imply that Magnums don't tend to run better at a richer or leaner setting because they have both a high and low speed needle is ludicrous. Every aspect of an engine, from stroke to bore to timing setting, ALL of these affect what it requires for fuel, what octane or cetane it requires, how rich or how lean it likes to run. If an engine unwinds substantially once it is in the air, it will require more fuel to do so, and if that "extra" fuel has not been accomodated by a richer setting, it WILL run lean, I assure you, whether it has TWO of EACH needle. Sometimes an engine uses the extra fuel to cool itself, sometimes extra fuel will heat an engine up. Those issues DO occur in this motor, and I assure you, those issues occur ESPECIALLY in this motor. It doesn't make the Magnum a bad motor. The Magnum is an excellent motor with a long life, as long as is it run rich enough. That is to say, plenty bubbly-sounding at full throttle on the ground.

Jim