engine missing/rough idle

While running our '85 nautique at 2500 rpms, you can here a missing. When you idle down, running slow, black smoke comes out. When you put it in neutral, it dies. As we took it back to the dock, it started running just fine again and lasted 3-4 hours before missing again. We trailored it and towed it home. We hooked it up to the hose and ran it here, it worked just fine?? Any suggestions?

My '85 was rough at the end of last summer. After 21years of trouble free boating with just basic maintainence it was time to give her some attention. After reading the forum, I rebuilt the carb and installed an electronic ignition (new distributor, coil, wires, plugs). These two things have transformed the motor. No more pumping the throttle on startup or rought idle even when cold. Combined with a new prop, exhaust hose replacement, and some work on the cooling system and even my wife said the engine ran as smooth as the GT-40 EFI in the Sport (not quite). You might try some simple work on the carb and ignition system yourself before having anyone else take a look.

85, From the black smoke you have described, my suggestion is to rebuid the carb first and then look at the EI if required.