O.S. 37 tuning problem

[tracerbob]

O.S. 37 in a stock Raptor V1, 15% cool power, O.S #8 plug. From a hover, we climb the heli straight up to about 30 feet and back off slightly to maintain altitude. As soon as he backs off the throttle slightly, the engine goes into this ring ding a ding (for lack of a better term) mode and then smooths out. Of course while the engine is acting up, the tail is jumping back and forth. The stick is at or around 3/4. It's kinda like when you rev up a dirt bike and close the throttle. We've tried tweaking both needles to the rich and lean side, and even swapped out the muffler and it still does it :arggg: Any ideas?

[Jafa]

You're lean on the low needle

Get the high needle on song during extended full power climb outs,
then tune the low needle for smooth idle and hover
Do a baby auto from waist high, in idle up
If you hear the ring ding ding then that low needle is still lean

Good luck with it