Need help with OS 50sx problem
 

I bought this engine new about 10 years ago and have flown it hundreds of times on my hanger 9 twist. Always prime right up and start with one flip. Always ran it on the rich side (like to see some smoke from omega 15%) New set of Boca stainless sealed bearings about 5 years ago still without play and new piston ring. . I fly this plane almost daily in the good months. Got it out and as usual prime right up and start on first flip. Now won't accelerate, just pops and stops when you give it throttle. Ran perfectly the day before. Checked tank, changed fuel lines. New O ring on needle valve. New glow plug. Check muffler pressure for clog. Richened it up nope! Leaned it out nope! Still will start right up and idle just like always but will not leave idle. Acts like it's too rich but it's not.
Anybody got any ideas or experience with this type of problem.

I have been flying that engine as a Hyper Heli engine for some 15 years and it's a great engine,, but boy you got me stumped, after what "Speedy" has told you I can only tell you more things to try,

even tho you say it starts well check head bolts and back plate bolt

loosen the Carb and push it down to make sure the O-ring is sealed well

how's the compression

BTW, back some 12 years many Heli guys found white colored plastic in their Carbs from manufacturing, but the plane Carb is different

Jim

I'm planning on doing a tear down as the only thing I can think of is maybe it sucked a bug or debris into the carb. This has been a very powerful and reliable motor and that's the only thing that makes sense since it performed flawlessly the day before. I'll report back when I get to the bottom of this.

Hi!
Have you opened the low speed needle some?