I have an OS91with pump that suddenly lost some power. I checked the valves and they are within spec. I noticed that when i turn the high speed needle all the way in until it seats gently, The engine still runs?? I have 2 OS 120 with pump and they are powerful trouble free engines. This one has me puzzled? Any ideas.
Thanks, Barzini

I am wondering if you overheated the engine at one time.  I did so to an OS FL 70, and I think that ruined the head, and it lost much power, which I never could regain.  I have an OS 91 with pump too, that I have only flown 5 times, but I got it used.  It's running fine.  You might want to ask Bax at the OS Engines Support forum here on RCU for help and tips.  Could also be something wrong with the pump unit.  Good luck.  Jon

Barzini,
i am not the best guy to give you advice,but i will try.

Loss of power may be visible if you lost compression,
due to an overheated run,
and destroyed the valve seals,so they don't sit flush on the burning chamber's head.
Assuming that all settings stayed the same before and after...
But,
yes maybe you should go and ask Bax!
I reallly like to know what caused that,because it's not that of a cheap engine

Konstantinos
Greece