Normally most zenith faults are cured by doing two things; stalling is caused by the idle tube getting partially blocked and the lower transition bores for the idle section getting carbon blocked. causes all sorts of weird symtoms.

simply remove both the idle mixture screws .generously spray carb cleaner to clean out the idle bores. next clean out the idle air tube . thin brass rod like 30mm or so. it can be accessed by removing the top cover .for later use mark out its air hole in the cover so that it can be sprayed directly without removing the cover.

start the car readjust the mixtures and all should be well.

regards
mak
220s
230
280s
300sel 3.5
300se 126