I assume you are talking about the Nelson Q500 engine, and not the Q40 engine??

As to fuel, Powermaster 15% Nitro is the fuel supplied to just about every National racing event. Locally, we run Omega 15% in Nelsons, and they run great. Cool power does not contain any Castor, and should not be used on AAC or ABC engines (some will argue this), but even coolpower does not reccomend this fuel for these types of engines.

I would suggest running a Bladder type tank with this engine. They run much more consistant, and do not run lean as the tank runs down. At full throttle you should be able to lightly pinch the fuel line and get a 400-500 rpm jump. No more than that is necessary unless you are turning a bigger prop. You should prop this engine to turn around 19,000-19,500 Peaked. The prop you mentioned should be in that range.

Other props to try would be:

APC 8.75" x 9 W
APC 8.75" x 8.75 W
APC 8.75" x 8.5 W
APC 8.8 x 9
APC 8.8 x 8.75
APC 8.8 x 8.5

All of these props should be available through Dave Schadell at www.pspec.com. Feel free to ask any further questions.