I have an OS 46 SF that I acquired from an estate sale (through a family in-law) so I don't have any history on the engine. I have flown the engine about 15-20 flights with no problems. Suddenly it developed a problem where it just quit running at full power. The engine seems to run fine below about 3/4 throttle but when it reaches full throttle then it just stops like a flame out, several dead sticks later we started trying adjustments on the ground!

I am a beginner but have had several "old pros" helping me (it has almost become a club project!). Thinking air leak, I've changed everything in the fuel system including tank and all new lines all the way to the needle. Nothing seems to work. There is plenty of fuel in the tank, no air bubbles in the line and I've tried rich and lean settings on both high speed needle and low speed adjustment, all to no avail.

To my knowledge the engine has not ever been disassembled and I'm trying to make sure I try everything prior to internal checks. Any ideas?

Thanks...
Bob
(second in command at YKnot Flying)

If the engine will run all day at partial throttle, but quit when you advance the throttle to full, it sounds like a fuel delivery problem. You may need to disassemble the carburetor to see if there's any kind of debris that would interfere with high-speed fuel flow. One problem could be an idle needle that's just too lean. If it's too lean, then it will interfere with high-speed fuel flow. Richen it a LOT, start at part throttle and see if you can get the engine to full. Get the top-end leaned and then go back and work on the idle.

If you can't get the engine set at all, you may have a problem with the piston/cylinder fit, although the idle usually goes bad first when you start to lose the compression fit.

If all else fails, the engine can be sent to the service center to be checked out.