Gotta love those Webers
You may be doing this already but one small suggestion, when jumping from one idle jet to the next, don't go more the 5 units at at time ie. 55 to 60, 60 to 65. In fact my best tune was a 62.
If I am following the thread correctly, it sounds like your tuning delima is in the mid-range or "transition" area in which case the idle jet is less significant. It seems like a similar problem I experienced and my air corrector jet made a difference in the transition along with the above mentioned timing information (found my distributer was timed wrong - made a big differenct). 2cents
Ultimately, the stars must be aligned
