I am not an expert on engines, but I am learning.

I have an OS 46 AX and it was in a crash a year ago. It hasn't been used much as it was prone to cause dead sticks. I have been working on the engine this past week to try to figure this thing out. This is where I am at so far.

The symptoms- It will start- It idles rough, then a little throttle and it smooths out, as I increase throttle from this point, it starts to die.

I changed the glow plug. No change.
I changed the high speed needle valve assembly with a brand new one I had laying around and no change.
I tried adjusting the low speed needle, it seemed to improve a little, but basically did the same thing- no change.
I took the engine out, built a test stand and mounted it with a new gas tank and lines, no change.
I have another OS 46 on a different plane that runs great. I switched carbs- no change.
I took the carb from the problem engine and put it on the other engine and it runs fine still, so that rules out the carb..

hmm.. now I am stumped- any ideas?

How the compression feel compared to the other one?

Not as strong as the other one. The other engine is new though, it only has maybe 15 flights on it. The one giving me the problem was my first engine and probably has 75 flights on it.

The compression seems okay on the problem one, but I didn't really focus on that, so I am not 100% sure. I just went and spun it over a few times and it appears to have good compression. I don't have a compression tester.

Reseal the back plate, check head bolts for tightness and new carb o-ring with some RTV sealer too.

What kind of fuel are you using? Oil% and Nitro %?

Is the muffler pressure line clear? The pressure fitting on the muffler itself too?

I know you changed the plug but what plug are you using?

I am away and will get home this weekend and check those things you mentioned. Thanks for the help!

yee-up, I agree, but first tighten all the screws, see what that does..


Jim

It is either air leaks or not getting fuel.  Since the carb checks out, check out the tank.  If it has a fuel filter check it to see it is clear.  But most likely an air leak. 

Chip

FYI Update-

I decided to go ahead and strip down the engine and change the bearings. Cleaned it all up good and made sure all the mating surfaces were clean, etc.

It's running fine now. Idle is a little rough, but should smooth out.

thanks for the tips!