DON'T adjust timing stop to change idle speed! There is a Idle Stop which can be adjusted to raise idle speed. You'll likely have to readjust the throttle cable for proper tension, after changing idle speed. Not to be confused with the "Throttle Stop" which is another adjustment for maximum carb butterfly opening.
There is an idle mixture screw on each carb, by which the mixture at idle is adjusted for, rich or lean. Adjust each screw for smoothest operation, idling in gear, fully warmed motor, in the water. Once you find the "extreme lean" range of each mixture adjustment, i.e. when you're screwing the needle "in" (Clockwise-lean) and the engine is going to die, turn the idle screw about 1/2 turn to the rich (CCW). This is a good basic adjustment and if you have a good "hole shot" without bogging down, pretty close. If the engine "bogs" upon acceleration after adjustments, turn each screw another 1/8-turn to the rich (CCW).
That oughta do it! "Spark Advance" or "Spark Stop" do not affect idle speed and should not be adjusted unless you're setting maximum spark advance. Get a manual for that.
HTH...........ed
