1986+ Mercury 6/8/9.9/10/15HP 2-stroke Factory Service Manual, Page 136Get this manual
FUEL DELIVERY SYSTEM
5Continue turning mixture screw clockwise until too lean mixture is obtained and engine slows down and misfires6Set low speed mixture screw halfway between rich and lean7DO NOT adjust leaner than necessary to attain reasonably smooth idlingWhen in doubt, set mixture slightly richer rather than too lean8Install access plug into opening in carburetor air intake cover
aAccess plug IDLE SPEED ADJUSTMENT (MODELS EQUIPPED WITH IDLE SCREW) 1With engine running at idle in Forward gear, make sure primerfast idle knob is pushed completely in and rotate fully counterclockwise to stop2Adjust idle speed screw to obtain recommended idle speedRefer to Section 1A