I have a 175 Mariner. It is bogging down underload, when I throttle it up in gear in the water. I checked the spark and it was giving me minor spark on three cylinders. Two on one side, one on the other. I checked it again at 3000+ rpms and it had great spark at the higher rpm. I just had the carb rebuilt. I checked the plugs and they did look oily and had some carbon build up. Could this be my problem? What should I look for. Also compression is good and I premix the oil and gas. Thanks