Engine starts and runs well but the exhaust is leaving a black deposit on the driveway. I pulled all 4 plugs and they are coated with a black "carbon" like dust. My trusty OMC manual suggests that this might due to a rich mixture in the carb and depositing burnt fuel. I installed new plugs, points, condensor, coil and had the timing checked last Fall. Also replaced last Fall was what I believe is called a float back valve - the line from the gas tank to the fuel pump. I did not have a chance to run the boat before I winterized it as I had to replace the starter selenoid. I have just finished replaceing the manifold and elbow. Is it possible that the deposit material in the exhaust and on the plugs is caused by a rich mix in the carb? Can I adjust this mixture on the carb using the throttle/idle set screws? Could the mixture be rich now because the fuel pump is actually delivering more fuel since the float back valve working properly? Would a different manifold effect the mixture in the carb? I know too many questions - I am used to working on just about all systems of this motor/outdrive but this is a new one for me. Until this season the exhaust and plugs have been clean. I have read that you can "live with" a rich mixture but I'd rather not be blowing this "soot" into the water if I can help it. Thank you for your help.
