I have a 15HP Mercury OB that when first started, appears to " cough", which is like a stuttering which then goes away after it warms up. This stuttering almost sounds as if the motor is shifting into gear, which I know it's not. One mechanic told me that the carb is too lean and to adjust the air screw 1/4 turn. I tried this with no luck. The only screw I can see to adjust is directly on the front of the carb(facing the gas inlet), just above the throttle plate area. Unless this adjustment is very sensitive, it appeared to not make too much difference. The motor will run/idle fine and then all of a sudden "cough". It runs great at WOT and after warmup. Could this have anything to do with the thermostat, or strickly a carb issue? Any help is appreciated!!
