koenig427

I have a OS .91 FX with a macs pipe and a fuel pump, I finally got the engine to idle great and run perfect, but with a 13x8 prop I cant seam to get anything higher then 9000rpm. Also it feels like there should be more power when flying at full throttle. Is there anything in particular I should be checking out to tune it better?

Also the pump was added due to the engine being mounted inverted and the carb being lower then the center line on the tank. With out the pump the fuel just pours from the carb.

Any information would be greatly appreciated.

Mike SVOR

My Feedback: (1)

Can you bypass the fuel pump and see if you get more rpm/power as a test?

oldtyme

I've just been going through this same thing. I'm running a 13x8 prop with 10% nitro and 18% lubricant fuel. Look at another thread in this section titled OS91FX advice and you'll see what was advised/confirmed for me. I think that an engine this size will only practically turn around 9000 to 9800RPM. Mine is taching at that range and seems to have plenty of pull. I"ve also learned that 10% id probably better than 15% for these larger engines.

Hope that helps,
Andy

koenig427

Well i fixed the problem by buying a OS 108 FSR. now i have a OS 91FX with a macs pipe and a pump for sale, engine runs great just didnt like the way i had it mounted. so i got a pitts muffler for the FSR to fix all the inverted mounting problems i had.

rcdude7

My Feedback: (264)

That "fix" warms my heart You can't go wrong with a 1.08fsr, that engine is a brute. Whoever it was at OS that decided to discontinue this engine, should be fired.