LokiDog,

If your carburator does not have the same opening at different times without having changed anything in the transmitter in regards to throws or trim, it is likely that you have a problem with the servo gears. The gears might be jumping one of two theets in both directions. I had the problem myself one time. I remember that idle was either too fast at times and too close at other times. Replacing the gears of the servo resolved my problems.

I hope it helps.

Pedro