Hot Dog! This motor is great now that I've got it figured out. I decided to knuckle down this weekend and spend some real time working with this engine to figure it out instead of taking 15-30 min stabs at it, like during the week. While the motor was showing some improvement, It still had way more shaking at mid throttle and idle than I was willing to live with, also I could only get a reliable idle at about 2800rpm. I'm using a new OS F plug so I knew I was in the ball park there. After a few mins I realized I hadn't checked the valve to rocker arm gap, it was waaay out...while I was at it I pulled the regulator apart and found plenty of junk. Nothing gritty but what looked to be brownish dried oil that was flaky and floating around in the fresh fuel of the regulator and around the lip seal of the diaphragm. So after cleaning the reg and adjusting the rocker arms, I put the engine back on the stand and it ran even better, but I couldn't get the idle any lower than 2400-2500 and I've read that the idle should be set at 2000. Up to this point I've been using the wood Zinger 16x8 and it pretty light so I thought I give the heavier Master Airscrew Classic 18x6 a try. Man , did the engine ever like this! Top end was 8100 and the idle was 2100, I could get to 2000 with glow heat but not without. The engine was much smoother across the whole rpm range, maybe the effect that the heavy prop has at absorbing the strong power pulses of the engine. The pull the YS has with the 18x6 is incredible! The only thing I need to do now is find either a hotter plug or add auto glow heat once the engine is on the model. Other than a Saito, what other plug is there to try? Mike.