Re: 25 hp mercury carb adjustments
If the engine idles (rough or not) you have a starting point. Slowly, 1/8 turn at a time on each carb, turn the mixture screw in. The engine may begin to smooth out and speed up which means the initial setting was rich. Or it may begin to slow and run rougher which means the original setting was lean. If the engine begins to smooth, continue turning the screw until the engine begins to slow and gag. Note the position of the screw and then go the other way 1/8 turn until the engine again smooths. Continue in the out direction until the engine begins to run rough and slow down and note that position. The best idle setting is somewhere between these two points. With the engine in the water (not on muffs because there is no back pressure) adjust the idle speed to spec. Put the engine in gear and go full throttle in one quick movement of the throttle. If the engine gags, richen (turn the screw out 1/8 turn) and repeat the process until it does transition from idle to full throttle without coughing or spitting. Finally, readjust the idle speed, in gear, at idle, to spec.
