Dave,

I seem to be having the exact same trouble with my ys 63 fz. Awsome engine at first.

I am running one on a top cap profile, with wildcat 20/20 and type f plug with a APC 13-4 wide. my engine doesn't seem to leak fuel though. I just adjusted the valves last night and ran engine tonight. I have a little better power now but it still loses rpm as it is held wide open in a hover, or testing on the ground. Running about the same RPM as above post, 10,300. I feel like I am banging my head against the wall. Is there anything I can try before I send mine in?

Thanks,

WOOD