just got a late 60s 50hp red band merc, i got it from a good friend whos pretty mechanically inclined and says it runs like a top untill it gets warm and then it gets real grumpy, he says he went over it well, carb pulled apart, new plugs, cleaned up all the ignition components, fuel is pumping, compression was good, but still says he thinks its an ignition issue, theres some sort of ignition box bolted to the side with about 4 coloured wires going to it tha he thought might be the issue. any help would really help THX!