1989 omc 4.3 starts runs 5 mins "clunk" dies

I recently purchased a 1989 Marlin open bow with a 4.3 GM / OMC Cobra powering it. Previous owner left drive down long enough to clip 1 inch off one of the prop blades. After installing a fresh prop, my first trip to lake had me overheating within 10 mins. Prior to overheat, started right up and got up and went when I hit throttle. Parked and swam with the kids for an hour and limped back to the trailer. after replacing the impeller and housing (prev owner had started it dry "just once or twice" I found out later) SO my second trip to the lake it started fine on the muffs at home, couldn't start at lake. Sounded like dead battery/cable connection problem. Took it home and pulled the starter off (as all connections and cables were good, pulled off wires and double cleaned what already seemed to be good connections. I had cables and starter tested at AUTOZONE, ORielly and NAPA. First two passed both cables and starter. Napa said starter failed. Upon checking with NAPAs computer (and my memory as I had gone through something similar with an 89 blazer) turns out the last guy had put the cheap $30 starter (non-gear reduction) in, so I replaced that with a gear reduction one and that seems to have solved the cranking issue. Now it will start fine.
OK, so heres the problem: starts right up, after 2-3 mins @ idle (neutral or in gear) I hear a clunk and the motor dies. Not sure if the clunk is in the engine compartment or behind the boat in the out drive unit. First time, at the lake, started fine backed away from the dock, spun around, put her into forward at idle and made it 1/2 way to the 'no wake zone' can. happened 3 more times getting back to the dock.
Then at home on the muffs, same thing. Started like a champ then dies about when you'd expect the thermostat to open....
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Any ideas on where to start? Manual wont be here till tues..

Re: 1989 omc 4.3 starts runs 5 mins "clunk" dies

My 89 4.3 cobra sat for 5 months (started it once a month for about 5 mins as I don't winterize it). When I got ready to take it out I started it and let it run for a little longer then 5 mins, and it died. Started up, died.. started up and it died. I wouldn't believe that gas would go bad in just a few months, but when I pulled some out it was brown. So I drained my gas tank (wasn't easy but I ran a tiny hose up the drain plug and into the vent opening. Replaced my Racon gas separator, put in new spark plugs (mine were blackened) and started the boat up.. Ran perfect. (until my shift cable broke, but that's another thread)

Re: 1989 omc 4.3 starts runs 5 mins "clunk" dies

Worth a try. I'll take a plastic tank from my old boat, clean out the 2stroke mix, fill her up and try that this afternoon. I'll update thread tonite or tomorrow. Thanks.

Re: 1989 omc 4.3 starts runs 5 mins "clunk" dies

tried with new fuel and filter and water/fuel seperator. same as before. It has spark and starts right back up, but again, dies in a min or two. Any other ideas? Replaced plugs while I was at it. Cap/rotor/points/condenser look new... Anybody?

Re: 1989 omc 4.3 starts runs 5 mins "clunk" dies

Classic fuel problem. I had something similar on mine. It turned out it was the fuel filter on the carb itself. Worth a try, remove it, put it back together and see if it works any better.

Re: 1989 omc 4.3 starts runs 5 mins "clunk" dies

This is a little bit of a long shot, but it is easy to test, and worth a try. I too would think it were a fuel problem, except for the "clunk", which suggests otherwise. One thought is, your resister wire from the alternator to the coil, is shot, and the wire from the starter sulonoid to the coil, to provide full voltage when starting, is staying on, and the clunk you are hearing is this disengaging. To test this theory, all you have to do, is test the voltage at the coil, with the key on, after the engine has "clunked" and died. (probes to positive side of coil, and to ground, not the negitive side of the coil) Again, it is kinda the perfect storm, but since you mention the electrical issues, particularly with the starter, this could be it.