John, try this trick that many use when setting the high speed needle. With the engine at WOT (wide open throttle) hold the airplane with the nose straight up. If the engine sags then you are likely too lean and need to richen the needle a click or two, then try the same thing again. If it sags or quits again richen the needle more yet. If you can't get the engine to hold a WOT setting while holding the airplane straight up even after this, then you can proceed to look for other issues. Also has the glow plug been replaced recently? Let us know what you find.