Looks like I'm not the first person to have this issue with the webra 120 carb:
http://www.rcuniverse.com/forum/m_32.../tm.htm#328677

In order to achieve transition, and in an attempt to have a non- rich idle, you have to turn the low speed needle in so far that there is NO gap between it and the spray bar. This would seem then to interfer with the high speed performance.

Perhaps the pump exaggerates this problem?

Yes, the webra carb has the high speed spray bar ending at the middle of the venturi, as opposed to the cat eye shaped slit of a super tigre.