Yesterday I mounted a 14x4 prop onto my Super Tigre .90. This is on my Sig Mayhem.

The engine ran considerably leaner than I've ever heard it run, and even though I gave it 1/2 turn on the screw, it actually flamed out in the air. I brought it back without drama. Tried again with a whole turn next time, and same result.

This has been the most reliable engine I've ever used, and I haven't touched the needle screw in a few years (it's been that good). I've never run anything less than a 6-pitch prop on this engine. At first I was baffled by why a diff pitch prop would throw the engine out of tune. But then in the middle of the night (when most revelations take place) it occured to me that it's because that flat prop isn't cooling the engine enough.

I was turning about 8,800 rpm with the previous 6-pitch prop, and it spun up to about 11,000 with the 4 unitil I gave it more juice at the needle. I think I'm gonna leave the 4 off.

Any thoughts?