The Stihl 64.9 works well but is heavy, didn't pull a 24-10 any better than a G62, and the stock carb has no high speed needle adjustment...I played around with a few of these, made from NIB blowers...Great sound, but for myself I would rather use a G62 or something comparable...
They run pretty hot, my hall sensor was mounted in a pressed on aluminum ring on the front of the case...When it failed from heat I made a ring from G10, problem solved....