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Engine wont turn off occasionally50 Merc

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crownline

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"'94 Crownline 5.0 L. merc

"'94 Crownline 5.0 L. merc. These first few times out this year boat is running well but has been a little harder to start and sometimes continues running after turning off ign. switch. I,m guessing its a fuel issue. Was planning on trying a higher octane gas and see if theres any change and go from there. Also I didn't change plugs since I've owned boat (2 yrs.).I can't get to them without removing exh. risers.Any tricks?"
 
Are you talking about engine &

Are you talking about engine "run-on" or "dieseling" ??? If so I think that's generally caused by (at its simplest) having too much fuel in the engine when you shut off the ignition. The condition is caused by there being enough fuel remaining in the intake to be ignited by hot zones in the cylinders. Eventually the engine vac pulls it all out and it stops. What i've seen cause it in cars:
Engine too hot(overheating engines can diesel)
Rich mixture
Stuck choke on fully warmed engine
Carb not closing all the way

If you pull it down to idle for a minute or two before shutting it off does it still do it?

Hard to start for my boat(4.3l) was a horrendously old water-sep filter and a carb body filter that had some gunk in it. HTH

--chris
 
"Idle speed may be too high. I

"Idle speed may be too high. It should be 650-700 RPM warmed up and in gear. Too high will promote run on.
The worst possibility with run on is sometimes the engine will kick backwards, and it will suck water up the exhaust and into the cylinders when this happens. Not good.

Rod"
 
To get the plugs out use a knu

To get the plugs out use a knuckle joint on the correct size extension. You may have to push the plug socket onto the plug while attached to the knuckle. Put a dab of antisieze on the plug threads.
 
"quote [Also I didn't chan

"quote [Also I didn't change plugs since I've owned boat (2 yrs.).I can't get to them without removing exh. risers.Any tricks?]
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I've also got a SeaRay boat hull design that makes access impossible. If fact, twice I paid for plugs to be replaced at dealers and they were still original plugs when I eventually pulled them myself! They could not get access either and decided since boat was running fine, to worry about it if I complained.

I believe my hull was originally designed for the 4cyl 470, but instead the V6 was squeezed in the hole. After I moved and had more time to do the boat myself, I found I had to take a reciprocating saw to the rear jump seat built-in inside-frames and cut away wood to get engine access from the sides. I have been doing personnal mechanic work all my life and still could not figure another way to gain access without pulling engine. Then I found the original oil filter had also never been replaced although I was charged for that too. It would not come out with the seat frames intact.

I hope yours is somewhat easier than mine was, but you might examine whether this cutting method is worth doing or even possible. Now it is a rather simple task to do this maintenance. I should also mention that I have since had to replace starter, which (while still not fun) would have also been impossible without pulling engine"
 
"Instead of cutting up the jum

"Instead of cutting up the jump seats, why not remove the retaining screws and install a "hairclip pin hinge" in the front for easy removal? Before my interior overhaul I just unscrewed the seats and removed them when necessary."
 
"Guy, the above post was stric

"Guy, the above post was strictly true commentary to substantiate the tight accomodations in some engine compartments. I would like to add that the way this rear hull seat is framed, it was not a matter of installing hinges, etc... The material I had to cut was part of the built-in structure boxing in the engine, not the seating biscuits.

I would not have cut it if there was any other way. But I certainly did not want to pull engine to do routine maintenance. Even two dealers could/would not replace plugs or oil filter. This hull design was revamped shortly after, but I believe was designed for a narrow 4-cyl engine.

I certainly do not recommend this step unless no other approach appears possible."
 
David:

Never mind me; my he

David:

Never mind me; my head thinks before I see the problem. You do what you have to do to get it done. I installed a bench seat in front of the engine and a HD lid for the engine w/4 SS rod hoders and 2 seat plates for fishing. Under the bench on one side is a very large livewell w/2 pumps. The other side is storage that never was there before. The livewell is accessed thru the hinged bench lid cutout and a sealed top to the LW. I cut holes in the back of the seat base on the engine side and installed 8" circular screw covers for access. I can't lay down nest to the engine anymore but can still get at everything.
 
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