Ric---The idle trim screw provides a very fine air bleed adjustment on
the ZS carb. Its purpose is to let a certain amount of air thru the
carburetor that does not pull fuel with it. If you're runnng rich, I
doubt that this adjustment screw would help. You may need to drop the
needle(s) deeper into the jets with your special wrench to make a
difference.
See the CDSE and SD-2SE section of the Haynes Carburetor Workshop Manual
for more on this. The Bentley covers this adjustment in somewhat less
detail.
Dick
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