The Zenith progression circuit was jetted lean and in particular the air correction jet for the progression circuit was humongeous at 160 vs. 110 for the non-smog IDA and 140 for the smogged IDTP which also suffers a lean progression flat spot. I have a modification kit to allow tuning the idle air corrector to help Weber IDTP carbs run better and the kit works on the Zeniths as well. It provides the ability to tune the progression mixture using idle jets as usual and using a tuneable air corrector jet similar to the main circuit and similar to the progression circuit design of IDA and DOCE Webers as well as PMOs.
Paul Abbott
Performance Oriented