86 OMC I/O will crank but not start

genenpet

Recruit
Joined
Jun 27, 2009
Messages
2
Got a starting problem and would really appreciate some help.

1986 Inboard/Outboard OMC (GMC) 3liter 4 cylinder engine will crank, but not catch.

Current: When you turn the key to "start" the starter motor engages and, if you push on the throttle, it will spin up and definitely ignite (engine will accelerate). However, the moment you move the key from "start" to "on" it just gently gently spins down (no bad noises, very balanced spin down). There is some gray smoke associated with the end of that process.

What we have tried:
1. Battery: jumped to bigger boat, changed battery, brought battery to store to be checked, no probs
2. Fuses: Checked the only two fuses we know about - two 50 amp fuses on the engine wires that come off after the power distribution point - we did have an electrical problem earlier in this process see below.
3. Fuel: Disconnected the primary fuel line and turned on the starter, saw fuel bubbling up. You can definitely see fuel in the carb when you pump the throttle too. Sprayed carb cleaner on the carb.
4. Spark: Checked spark at coil (not with tester, but just against the block), replaced all plugs just for kicks, had no impact.

What led us here: This problem came after another fix. We had replaced starter motor - new one worked four times, then big sparks and grinding, blew some fuses - opened it up, saw lots of pieces of the starter motor plunger shredded and sitting in the area where it engages the flywheel - cleaned those out. Replaced again, new one seems to work, but now engine won't "catch". Again, this problem did not exist before - she had been running fine previously.

All help greatly greatly appreciated, we have houseguests from China this weekend that my wife has been promising a boat trip to for months now... always the way... Thanks in advance
 

Ridemywideglide

Petty Officer 2nd Class
Joined
Jan 13, 2009
Messages
166
Re: 86 OMC I/O will crank but not start

Run a temporary wire from battery positive to positive side of coil, then try to start. Do not leave it like this for very long while not running.

It sounds like your losing ignition power when the keys turns back to run.
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
71,241
Re: 86 OMC I/O will crank but not start

Ayuh,... Sounds like you screwed up the wiring on the Starter during the changes....
The Key is not supplying power to the Igntion...
 

genenpet

Recruit
Joined
Jun 27, 2009
Messages
2
Re: 86 OMC I/O will crank but not start

Thanks - this was exactly what the problem was - we thought we had ruled this out early, but we had done something wrong. Specifically (just in case this helps someone else), the starter coil has the two wires we were clearly getting electrical flow from the "on" wire back to the starter motor even in the on position - causing the starter to motor to engage even when the key was not in start mode. It wasn't until we got the jumped battery wire that we heard the scraping and thus figured it out. Thanks so much for the replies.
 
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