When I hold the plane vertical with engine idling, RPM would slowly decreases and eventually the engine quits. I see a few bubbles in the fuel line before the engine quits.

The low-speed needle setting seems right. When I pinch the fuel line at idle, the RPM would increase after 4~5 seconds. I tried richen and lean the needle, but the engine still quits whenever I hold it vertical.

I set the high-speed needle slightly rich so that when I hold the plane vertical with full throttle, RPM would increases a little.

Are there any other tips for engine tuning? Right now I'm using idle/full throttle pinch tests to determine my needle setting.
Thanks a lot!