some problems, any advice please. the symptoms are. engines start up and purr like kittens. but after about half hour port engine starts to die off. sputtering and rpms dropping untill shes dies completly. starbord runs fine and gets us home everytime. so could this be a faulty coil? or what should i check for?

You could swap coils on the motors and ignition boxes to see if it follows before you start spending money.
Mike

should also be able to change sensor without disturbing dist. However timing should be at least checked after changing module or sensor. I've seen the hall effect sensors cause this same crap out problem on cars. BBB

could a plugged fuel tank vent cause these problems as well?

Gremlins......

I had similiar couple years ago, would go out and after a while starboard would die out, let sit for a while and would re-start and do again. Turned out to be the harness quick connection. had some corrosion and with heat and movement of boat would lose spark. Try pulling the quick connector apart and inspect inside.
good luck

I think that your first thought was best. When coils start to go bad they begin to break down when they warm up with use. Do like goob says and see if the problem follows the coil. A sensor usually quits completly and never comes back. Seen this often with T-Bolt IV's (I assume that is the ignition you are running) and it's always been the coil. --- Jer

thanks a lot for all the input. did not have time to work on her today but, should be at it tomorrow. now if the coil does need replacing is there a better type to use or should i stick with the merc stuff?

I have been using MSD Blaster II for the past couple years with my T-Bolt IV and the V8-HP (20 deg. adv.) module. Couldn't be happier! --- Jer

ok we checked the coils and swaped em for ones that were good. and the problem returns. the engine starts up fine and runs smooth. but after 20 min. she starts to sputter and cut out. what should i look at now! ignigtion control unit or something like that?