I have a Cline Modified Tarten Twin (glow / 0 nitro) which has never really given too much trouble.......I have until an unfortunate landing run a Bolly Carbon Fiber 19x10 prop which the engine would turn about 84-8600......Which is really the sweet spot..............

Now that I'm waiting on a replacement prop..I've tried a few others...
A Zinger 20/8 wood which only turns about 7300 ?????
I also tried a Zinger 20 6/10 and cut it down to 19 and could only get 7300 rpm..Both really load the engine and it runs hot...

.Why would a light wood prop turn less rpm ??? I'm going to try a zinger 18/12 to see if it will go 8000 ....

I've gone so far as to add more oil to the fuel (alcohol) to see if it will help disipate the heat..No help ...........

The Bollys are a little hard to get for me....Any suggestions on any other props or combos to get the RPM up......This engine is on a 30% extra.