hi, guys i got the same as said by you all, i spent two years on and off troubleshot the problem, finally i have found the fix for mine. there were two problems that i have spotted on mine. one is the fitting in the carburator thatlead to the high speed needle valve and the one mounted on the carburator itself . those fittings are loose and the washer that came with not sealed good the air leak into bubling in the low speed and fuel dripped on and off. i jbweld those also change my silicone tubing into the medium size for tightened grip onto the fittings. i used prop 16x4 apc high rpm reached 9500 and the low speed in the range 2000rpm. i flew my harrier with great success.

jim s