I have a 1976 evinrude 15hp (15604A) motor that just recently started running rough, sounds like it is not running on both cylinders and not having full power under load. When running and I pull the lower cylinder plug wire it runs a little rougher and when I pull the top cylinder plug wire is runs very rough and dies out. I switched the ignition coils around and pulled the plug wires again one at a time and it does the same thing. I cleaned and set the gap on the points to .020 and still not running right. Any help with a solution here is appreciated.