Boat “runs on” when shutting off after a long cruise then won’t start

[scott8058]

95 bayliner 2050ss
5.7 merc cruiser with alpha one

So after we take a 15-20 cruise then come to the beach if I don’t let it run for a min or two at idle it won’t shut off and runs all clunky sounding. If I turn the key back to on it starts right up. today and one other time I tried turning the key off like 4 times before it quit running. About an hour later it sounded AWFUL and wouldn’t start for us. Some guys from the beach thought it was starter teeth or flywheel and we kept turning the motor by hand and re trying it. We took a plug out and no water came out and eventually got her started and got back home. Just like the last time this happened a few hours later at home it started like a dream on muffs. If it only does this run on once and I get it to shut off it is fine. Any ideas why it won’t shut down? Timing maybe? Also what is going on when it won’t start back up? When it doesn’t everytime I try it gets closer and closer and closer and eventually goes back to running fine. Any help is appreciated

 

[nola mike]

Dieseling from timing, running lean, running hot. Always a good idea I think to let the engine cool off before shutting down. You're likely having reversion and water entry into the engine (did you pull all the plugs or just one? ).

 

[scott8058]

Just pulled the one plug, so I should look into fixing the timing on it? Also so did all the times of cranking it push it out? Thanks

 

[Bt Doctur]

Hard starting after dieseling can be hydrolock, too hot, to lean too fast , too much advance need to be addressed

 

[Boater31]

Don't forget idle rpm being set to high. Also the throttle linkage at carb should be checked to make sure it's applying slight pressure at idle.

 

[Scott Danforth]

that death rattle at the end when a motor diesels is the motor actually running backwards and sucking water from the exhaust

change your oil it will have water in it.

fix your timing and check your fuel system.

usually dieseling is from the carbon deposits in the engine glowing red hot, like glow plugs, and your motor continues to run. its normally caused by running just a tad rich and having too much timing. having a high idle will also contribute.

you can turn it off in gear which puts enough load on the motor it will shut off. however best to find the source of the problem and fix it.

 

[Bondo]

that death rattle at the end when a motor diesels is the motor actually running backwards and sucking water from the exhaust

Ayuh,...... Exactly, I came in here to post just That,......

Yer lucky you haven't bent a connectin' rod,......... Yet,......

It starts hours later, 'cause the water has seeped pass the rings, into the base,.....

 

[QBhoy]

Almost always caused by water in the fuel.

 

[scott8058]

Thanks for all the responses guys, I will get right on it and start with the timing and idle as it was idling high that day when we cruised into the beach. I feel like I need a new carb as a couple years ago when the boat was overhauled the carb was pretty bad but we just cleaned it up really well instead of buying new.

 

[QBhoy]

I’d honestly be looking at the possibility of water in the fuel before messing with anything like timing. You’ll only have to go back to do the same if it is water. Just a thought.

 

[NHGuy]

I disagree about water in the fuel. When my 87 5.7 did it the timing was too advanced, the idle was too high, and the risers were leaking water into the exhaust.

 

[Rick Stephens]

Gotta check timing, fuel and mixture or this will happen again next time the operator has to shutdown while maintaining headway, and lifting drive, heading in to beach. Scary easy to lose a motor sucking water when dieseling