I recently purchased a slightly used O.S. .46AX. I installed it inverted in a Seagull PC-9. The centerline of the fuel tank is approximately level with the carburetor. I also installed a Great Planes quick refueling jack in the feedline. The jack is approximately 3/4" above the centerline of the tank/carburetor.
The engine cranks very easily and has a low and steady idle. However, I am running in to problems when attempting to adjust the needle valve according to the owner's manual. I am finding that the engine reaches maximum RPM with the needle valve within a few degress of fully closed (clockwise)! Otherwise it stumbles and hesitates when the throttle is opened fully. It revs fairly smoothly after adjusting the mixture control valve slightly clockwise from the factory setting.
Is there something I am doing wrong here? I have used other O.S. motors in the past and was able to tune them according to the owner's manual.
Thanks!