Jake,

If it's not fuel, needles, or valves, it could be as simple as the plug. Check it again.... I know you said you replaced, but sometimes they go bad right away. Also, a small trick.... pull the element down a tad with your xacto blade. I would also state that this motor is happier at mid 9's for RPM vs. mid 8's..... however, with that said I ran a 14/10 APC on my motor at 8.9 to 9.0k at the last race and my motor was very happy on 20%.

If you want help tuning I'd be more than happy to work with you on set up at the next race down at SAMS or when your back in Sacramento.

I just went back and looked over your original post and I see two things in it that I feel need addressing. First, I've found that Master Airscrew props are a lot harder to tune based upon how the "flatten out" when you run them up and restrain the plane. This is my personal opinion, but from what I've found it is easier to tune a motor using an APC prop. Secondly if your running rich like your 1st post leads me to believe you may have damaged the plug element right from the first run after replacement.... take it out and compare to a new plug.

Lastly.... I would add to Iron Dog's prop suggestion..... The two props I think are good on this motor.... APC 12x13N (I won a lot of races with this combo), and the out of production APC 13x12N if you can find it (this is the prop that APC MADE FOR THE .91).... I have few of these left and for sport flying love them on my Mustangs and Spitfires..... but I must admit, I'm pretty happy with the 14x10 and the "gas mileage" has gone up.

Take care,
Jimmy Skids