I have a 1976 evinrude 9.9 modle 10624H. It eats up spark plugs like crazy. If I put in a new set of plugs (marine champion Ql77jc4) motor will run great for a few hours 2-4. Then motor will feel as if its loosing power and when put in nuteral and reved up it is slow to get to full throttle as if there is a delay. But when u pull the plugs out and replace them it's like a new motor. I have tried cleaning the plugs but nothing, it's like they are destroyed and cannot be used again. When I pull the plugs out they are not wet or oily as if they where getting fouled. they look like a normal plug with a little black carbon on them. Any thoughts???????????????? I have also tried diffrent brand plugs with the same result.