I have an RCV91cd that I've been flying for some time now (after getting it back from repairs from the UK). It's really been running very well, starts easily, good high end (about 9200) and idle (about 2400) and never had a deadstick. But last week that changed. I'm not sure what happened. It still starts easily but it won't rev about 6000 and if I open the throttle wide it dies. Also telling is that adjusting the needle doesn't do anything. It seems to be running lean, though.

A mate suggested there might be some junk or grim in the carb so I flushed that out with an alcohol-based parts clearer spray, but that didn't solve the problem. On the test stand, I started the engine with the needle about three turns out but even at this rich setting I wasn't getting much smoke. And as I screwed the needle in there was no change in the RMPs until finally the fuel was cut off and the end stopped. In short, adjusting the needle valve doesn't seem to do anything at all.

What's happening here?

Hi!
It's much easier to just remove the needle to inspect if there is any dirt inside.

The needle looks clean and I flushed out the carb barrel area also. I can't see any grit.

Look at the lines and the tank. Sounds like a hole in the fuel line. Make sure all engine bolts are tight. A loose backplate also will cause your symtoms.

I'm not familiar with whatever engine you have but what you describe could be the result of a worn O ring on carb or needle valve. It seems like you have lost suction from fuel line.

Thanks for all the suggestions. I still think it's "gunk" but if not, I'll check all these other things. Now's a good change to change out all the tubing anyway.