Another posibility

I haven't run the new pumped webra120 but I have 3 of the old webra120s. Webra uses the taper on the idle needle to control the mid range mixture. I have generally found the mid range would be too rich unless the idle needle was set very lean (right at peak) if the tank was located at about 1/2 inche below the spray bar. With a pump tank hight shouldn't matter but the idle needle still may be something you have to screw with.

Denis