I have rebuilt both carbs, Zenith INAT 35/40s, sync'd AND set per the Jamiekop manual. Issue I have is the rear carb idle mixture jet makes no difference when adjusting. Changed to a different carb and have same issue. Front carb will idle down and stall when turn the idle mixture screw in. All passages are clear and vehicle will stall when covering the inlet with my hand. I'm a 40 yr plus working on cars, 10 yrs retired. I'M STUMPED......

I don't know this car specifically but some dual carb systems idle only on one carb with a small balance tube / intake manifold passage between the two. The screw on the rear carb you are turning, is it an actual pin point needle valve or something larger?

The idle on one carb of 2 was used on 72-3 ish VW Bus. This and single carb engines use a idle mixture strength needle valve and an air bypass screw to set idle speed. With these, the throttle stays nearly fully closed with the idle circuit acting like a mini carb.

Yes the screw is the actual idle mixture screw, the one that leans/riches mixture. The intake has a balance tube and the hose that is attached goes to the air cleaner when installed. Right now I have it blocked off.

Not my car but the same style W114

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All valve train in proper order and condition ? Cam timing correct ? Vacuum test correct ? Engine leak down test positive ?