My brother just gave me his boat with an 1988 Evinrude 88 SPL motor on it. He ran the motor fine last year & not at all this year. We dropped the boat in the water, it starts ok, runs a little rough but stalls when it is shifted into gear. I changed the plugs, checked/cleaned the fuel filter and used new gas. The problem still persists. I can get it moving at very slow speeds if I press the prime when it feels as though it will stall. The carb appears clean, and the prime bulb is semi-hard. What else should I look for? Thyanks for any assistance.