Then it sounds to me like the low end is too lean.
The low end should be set a little richer than what might seem as ideal on the ground, it is set for a good throttle response in the air (no hesitation) and a less sensitivity for a lower fuel level in the tank, and/or a plane in a slight nose up position.

The high end might also be a little too lean. If there is no reaction to the pinch test then it will be too lean when it is in the air. You want to have a little increase when you pinch the fuel line, to make sure that it does not run too lean in the air.

(just to clarify an engine will usually not run on idle when pointed straight up, but when going from level to an inclined position the low end will go leaner and the engine should rev up a little rather than just dying.)