Hi,

I'm getting back into RC flying after the interruption of starting a family. I have an ASP .61 that ran great back in the day but has been sitting for 13 years mounted on a Big Stick. I took the engine apart and cleaned it up and it started right up. I didn't have any trouble getting it to run up or idle so I headed for the field. I started having problems with the first flight. When the engine was running wide open, It would lose power and not die immediatly but sort of idle and would run up if I cut the throttle way back It was kind of like running out of gas. I was able to reproduce the same behaviour while static in a yoke on the flight line where wide open for a while it would get into this mode where it lost power and would only stay running if I cut back on the throttle. At this point I started having trouble adjusting the high speed needle valve. It became real stiff. I discovered that the O-ring on the needle valve was shot. I had some trouble finding another O-ring and the one I settled on doesn't fit as well as the original. I still have the problem to some degree as before but I noticed another thing that may be a good clue for someone who knows about engines. When running wide open at about a half turn away from too lean, if I pinch the fuel line, the engine cuts as expected but it cannot recover when the restriction is removed. It shows the same symptom as above where it stays at almost an idle and the only way to keep the engine from dieing is to cut the trottle and gradually increase once RPMs pick up.

Can anyone tell me what I may be looking at here?

Thanks,
Marc

Unless you replace all the fuel lines including the ones inside the tank and use a new tank stopper, you will be plagued with mystery

Is it also a 13 year old glow plug?

Welcome back Marc!

Not long abgo, I had a similar problem.
I believe your engine is not getting enough fuel at high rpms, in other words, the engine sees a lean mixture at high rpms.

As w8ye stated, there are many little things that may contribute to that, from the tank to the spray bar in the carburator.

Check for two things:

Air leakeage into the crankcase and carburator: This could be from harden gaskets, needles, barrel, flat bearings, etc. I suggest to check / replace all you can.

Fuel blockage: From gum and hardened oil inside the spray bar, nipples, etc. I suggest to soak parts in fuel for some time, and blow with compressed air. Do not use wire or any metal tool.

The o-ring you mention is highly suspicious. You could help it with teflon tape applied to the thread.
Diassemble the spray bar and blow in the opposite direction in order to detect air leakeage thru the o-ring / thread.

Use a new glow plug and new fuel.

Regards!

Make sure the muffler nipple is clean as well.  You will get a lot of gunk there on stored engine.  This can cause muffler presure to the tank to fluctuate causing mystery problems as well.</p>

An old friend of mine would say, "Check the fuel  system."  He was almost always right.  Old dried up stuff in your tank from its days of rest may be your cause.  And it sounds like a partial blockage to me too.  So, yes, check out your tank from clunk  to the carb.  Could be in the carb now, if it was a piece of dried up crud floating around from  the tank.  So  clean her out begoinning to end.</p>

Cheers,</p>

Chip</p>

Guys,

Thanks for all your suggestions. I began by ordering new o-rings for the carb. Idid blow and clean everything out when I disassembled the engine but it did not occur to me that new gunk could have entered from the tank. I'll open up the tank and replace the tubing and make sure that's all tight.

I'll let you know what happens.

Marc