"Hi Mark, I have an 87 1750SS
"Hi Mark, I have an 87 1750SS with a Ford 2.3L and Cobra outdrive, so i'm guessing we have pretty much the same boat.
My operators manual says...
Changes in fuel, altitude and climate may make it necessary to adjust the idle speed and idle mixture to obtain smooth engine operation. Before attempting to adjust carburetor, ensure the backfire flame arrestor is free of debris, dirt or grease.
(Note) Carburetor idle speed and mixture adjustment should not be attempted until engine is warm and it is known that ignition system (inc spark plugs ) are to specifications. Any attempt to alter the carb to compensate for faulty conditions elsewhere will result in reduced fuel economy and overall performance.
With someone at the controls and the engine warmed up, run engine in forward gear and adjust the carb idle screw to obtain specified rpm (600-650 in forward gear) Turn the idle mixture needles, one at a time, in or out, until engine runs smoothly. Ensure specified rpm idle speed after readjusting idle mixture needles. Final adjustment should be with the idle mixture needles.
If your engine still fails to operate smoothly, or if the specified rpm idle cannot be attained, see you OMC dealer for further adjustment.
(Note) Do not attempt to increase idle speed except by the above procedure. Excessive idle speeds may result, causing damage to the gearcase during gear shifting maneuvers.
This is taken directly from my operator manual, for information, the idle mixture needles are the two screws at the bottom on the side of the carb, one for each barrel. The idle stop screw is the one that screws against the throttle linkage.
Hope this helps
Barry"