Check out the idle circuit on each carb by locating the idle air hole on the front top of the carb, and plug it with a pencil eraser. If the warm idle falls, then the idle circuit is OK.

If the idle doesn't change, then try a "hand job" to unplug the idle air passges. Bring the engine up to 2500 RPM or so and put your hand over the primaries. You will fee the suction on your hand as the engine starts to die. But it will force air through the idle circuit and may unplug it. Repeat a couple of times.

If the car is otherwise running well and warming up without backfiring, I would avoid the temptation to rebuild the carbs or adjust them. About the only wear parts are the float valve and the accelerator pump and they are easy to check.

I would leave the carbs alone for now. We have seen a number of Zenith problems start with a rebuild or adjustment!

__________________
Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe