1985 OMC inboard / outboard engine dying

[bama45chap]

I have a 1985 Chaparral that has spent most of last year in the shop. This year already started off badly. I bought this boat new in 1985 and it is in mint condition. However, last year I started having problems with the boat misfiring and then when I shifted it into neutral it would die. Sometimes I can restart but it will die immediately after shifting into gear.

I took it to a reputable service mechanic and we've replaced the plugs, plug wires, points, coil, reworked the carburetor and still the same problem. Now it fires off perfectly but after running say about 30 min. it begins to misfire. That when it will eventually die if we don't stop. When we stop it does die almost immediately and it will not run until it cools down. It isn't really getting excessively hot but something must be heating up that just won't run. It can not be anything major as we've replaced all the major things. Our mech. consulted with another mechanic and they even clipped from the positive side of the coil to the positive side of the battery after the boat died and it fired off and ran perfectly all day. Great results but that isn't practical with children in the boat. However, they still haven't been able to pinpoint the problem. This year I went to an automobile mechanic and we ran on the lake in March. The weather was cool and I had the cover off so it would be easily accessible and it never behaved badly. He suggested changing the spark plug wires and that resulted in great cranking but still same problem on a 90 degree day this Sunday afternoon.

Has anyone ever experienced anything like this? I would appreciate any input! We're at our wits end on this one!

1985 Chaparral
GM OMC inboard/outboard
3.8 v6 175 HP

Thanks!!

 

[Howard Sterndrive]

Re: 1985 OMC inboard / outboard engine dying

Need to measure voltage at the coil + when it's acting up. Sounds like the resistance wire to the coil is breaking down. (purple/red wire to the coil +) It gets pretty hot in normal operation so it tends to not live 25 years.
Could also be the ignition (key) switch in the dash, or any loose/corroded wiring connection in between.

Many of the things you mention being replaced, like points and plugs, are actually supposed to be replaced every year.

 

[bama45chap]

Re: 1985 OMC inboard / outboard engine dying

Thanks for your reply. We actually have replaced the resistance wire too. One more thing replaced was electronic shift control module. The boat is garage kept and serviced every other year for routine maintenance.

I can't get the boat mechanic to go with me to the lake. He just tries to fix by putting the ear muffs on the boat and it's hard to get it to misfire without putting the load on it like you do when in the water. The only mechanic that would go was the car mechanic. Guess I'll try to get him to go back with me and do as you suggested about measuring the voltage.

If you have any other thoughts, I would be most appreciative!!

 

[wire2]

Re: 1985 OMC inboard / outboard engine dying

I believe this is a stringer, and not a Cobra? There's a micro switch on the shift converter cover that actuates the shift assist module. Check to see that the white switch button is in the center of the detent when in FWD or REV. If it's on the verge of being depressed, heat may cause it to trigger the assist module. That will make the engine stumble and possibly stall.