Hi everyone

I have an OS 50SX in my H9 Ultra Stick. Lately, the engine has a very high idle, and quits when I pull the throttle trim down. I've checked the fuel tank for air leaks as well as all the fuel tubes. What can I do to get the idle to normal. At the moment it is too high for a safe landing with the engine running.

Any suggestions would be welcome.

It really sounds like the low speed needle is too lean.

If not the servo/carb link needs adjusted

Since you said "lately" I'm assuming it ran fine before, but just started giving you trouble on the low end. If thats the case, replace the glow plug.

Brad

could have picked up speck of dirt too.

Yep, sounds like a glow plug.

I've tried two new glowplugs with no effect. I've also richened the low end needle to the point that the throttle response is slow and bumpy. If i made it any more richer the throttle response would be too unreliable. I have tried a No.8 and an A3 OS glowplug in the engine. I'll remove the carb and flush it properly, before i try again.

Air leaks can come from the carb-to-crankcase seal.
Are the carb screws tight?
Is there an O-ring between the carb and crankcase, and is it in good shape?
Is the throttle barrel loose?
Is the throttle limit screw still there? It's spring will often let it vibrate out since it's not a screw that is tightened against anything.

How many hours on the engine? Sometimes they'll lose their idle if they've varnished up. They usually only varnish up when you're using castor oil fuel, however.

And sometimes it's something you're not even looking at. I just helped a guy with the same problem and it turned out that his throttle pushrod was running into a bulkhead. He had some bends in it and one of them was bumping into a bulkhead. It would go to full movement on the ground but was intermittent in the air. I guess vibration helped sometimes or hurt sometimes.

What is the RPM at idle?

Bill

Is the compression still good?

It may be a mechanical problem. The servo tray may have come loose or the throttle tubing that the push rod is in. A quote from another thread on this same problem " Yes, I have seen the screws fall out before.(carb screws) Had a guy out the other day and we just could NOT get it to idle down no matter what we did. Throttle closed and even with a finger carefully placed over the intake the silly engine kept running, quite fast at that. We looked at what we thought was everything and finally noticed one (1) of the 2 mounting screws had come out. this allowed air in and the the carb supplied fuel as needed to run. No spare screws on the field that fit so he had to park it for the day but at least we had figured it out.
[8D]

Have you tried leaning the low end? A super rich low speed will cause the carb to load up quickly and kill the engine. Good rule of thumb is if one adjustment direction to the extreme doesn't help, go back to your original settings and try the other direction. Also, make sure you reset the high speed needle after every air bleed adjustment.

Brad

Is this the same engine that you have been having trouble with since January? If so, did you ever get it running totally properly, just so we'll know.

Bruce88123: This is the same engine, but I have replaced the piston ring and now the compression is much better.

I've found the idling problem too. The carb had not been pushed down completely into its seat on the crank case, rendering the o-ring useless. I pushed the carb down firmly into position and checked that the o-ring made a good seal against the crank case. Problem solved!!

Thanks for all your help!

Yep, extra equals extra RPM. Glad all is well.

the idel screw on the engine is not set right then un-screw it just a little bit and u will be fine