ORIGINAL: earlwb
Usually with a tuned pipe, you have the problem of the engine unloading in the air and rev'ing up more than it does static on the ground.
So it may be leaning out in the air on you.
My old method was to tune the engine on the ground with a prop with 1 pitch less than the in the air prop I use. For example if I used a 11x7 prop in the air, I would tune it with a 11x6 prop on the ground. That would get me closer to the needle setting needed for in air flying.
Later some engines had a second servo operated in flight mixture control that one could use to tweak the engine in the air too.
But in any case you may be a just little too lean when the engine unloads more in the air on you than it does on the ground.
Yup, that might be part of it. When it first started, we found that it was good with a 13 x 6.5 on the ground but couldn't get a good read since it started with it's surge.
This past weekend, we changed a couple props looking for a good match to the pipe and the 11 x 7 was best out of what I had. We did lean the low end just a tad and it hit better so perhaps we went just a little too far.
I'll have to do a little wing repair from this past flight. The thing just will NOT slow down and it sailed right past us when it did dead stick. Ended up in some rough turf and tweaked the left wing. I've got to unsheet some of the wing and fix up the wing tube socket / box before I fly it again but I'll give your suggestion a go.
Oh yeah, did have the adjustable carb on it to begin with but replaced it with one without the adjustment. It's got a plain 86 on it now. Running a 6 channel rx and just didn't have the servo space.
Thanks.