ORIGINAL: soarrich
ORIGINAL: KenVW
my prop is 17x8, we flew a buddies last nite which I set up for him, it had an 18x10 (same engine & plane) ran great.
Try switching props with your buddy, see if the problem goes away or switch to his plane, then go from there.
Or switch carbs AND props? That would cancel the main differences. If the problem remains, the engine might be sloppy in the bearings or something like that, so that at higher rpm, air can bypass the carb system, or the pulse line from crankcase to carb is obstructed / loose.