I have a 1988 mercury classic 50 45hp. Most of the time it will not fire the top cylinder. The top rpm is about 4200. Then at times the top cylinder will fire and get up 5200-5400 rmp. I have used an inline spark tester which shows the problem. I have also switched the plug wires and plugs but top cylinder always has the problem. My guess is that the coil is bad, but is it possible that it would work sometimes but not all the time. Does anyone have any thoughts on this. <br />Thanks, <br />Mark