I just recently had a coil go out on my 50HP Mercury. I got a brand new coil and put it in and now have lost around 10MPH at full throttle. I have also rebuilt both carbs and changed the plugs but no improvement. My thought is the new coil is bad. Is this possible? I hate to spend another $50 on a coil just to see if the top end speed improves.
I am past the return date on the coil being it took me all summer to trouble shoot the problem. I first thought it was a carb, then the coil, back to the other carb and then finally the coil. The problem was so infrequent that it took all summer to pinpoint it. When I put the old coil back in the motor runs great for about 30 seconds then goes to running bad again. So it has to be the new coil, right?
This is what I have done. I have checked all the wiring and it is looking tip top, I tightened a few loose wires so good to go. I checked spark on each cylinder and have good blue spark coming from the plugs. I decided to check the compression and have 120 on each cylinder. I checked the wires on the stator and all look good. Does anyone else have an idea on what to check? I am still not at full power and the only thing I can think is trying another coil.
Fuel lines are new, both carbs are brand new. I have new clean fuel, good spark, good wiring, and good compression. I am at a loss, any help or thoughts is appreciated.