Engine won't stop even if turn off the start key.

[sea mania]

I own a 2007 Regal boat.
The boat engine is Volvopenta 4.3 gl.
An engine equipped with a holly 2 barrel carburetor.
The problem is, if I turn off the key to turn off the engine, the engine will shiver for a few seconds and then stop.
The engine is normal only when it comes to a stop, but the engine has not stopped even when the starting key has been turned off.
What's the problem?
Please help me.

 

[jimmbo]

Welcome to iboats
In one sentence you say the engine does stop, then in the next sentence you say it doesn't stop. So which is it?

If the engine isn't shutting down, a bad switch, bad wires, and/or incorrectly wired circuit could be the trouble

 

[sea mania]

I'm sorry.
I mean, if I turn off the start key, the engine won't stop immediately.
It quivers for a few seconds and then stops.

 

[Scott Danforth]

that is called run-on..... which is usually caused by bad fuel, or the motor is running hot or the timing is too far advanced.

that shudder at the end, is the motor actually running backwards and sucking in water from the exhaust.

if you just pulled a skier, and are shutting down, let the motor idle for a bit.

buy good fuel
verify your timing
make sure you have correct spark plugs
make sure your engines cooling system is in perfect shape.

however you need to fix the problem before it costs you your motor.

 

[sea mania]

Thank you for your reply.
Contrary to your concern, my boat cooling system is perfectly normal, and fuel has always been used as genuine fuel.
The idling speed is normal.
So I can't guess what's wrong.
Can you explain what you mean "the timing is too far advanced"?

 

[Bt Doctur]

engine temp under 165?
genuine fuel is fuel rated at 89 octane
too lean of an idle mixture
idle speed under 850 in gear, in the water
ignition timing has changed, too advanced ,or dist advance weights stuck advanced

 

[harringtondav]

I had the same problem with my Merc. 4.3 4bbl weber. The problem only happened when I shut down right after coming off high speed. Idling for just a minute cooled it enough to stop the problem. I fixed it by trial and error adjustments with the idle mixture screws. I think I was too lean.

A short term fix is let the engine idle for a minute, or shut it off in gear The extra load normally kills it immediately. But as SD said, fix it before you suck water into your hot exhaust manifolds.

 

[muc]

or shut it off in gear

Don't shut off a Volvo or MerCruiser Bravo in gear. It might not come back out of gear.

 

[jimmbo]

Don't shut off a Volvo or MerCruiser Bravo in gear. It might not come back out of gear.

Never had any problem the past 17 yrs

 

[muc]

Never had any problem the past 17 yrs

I have been paid to fix the boat many times in the last 25 years after somebody did this. Can also rarely happen when shifting a Bravo while the engine isn't running.
Doesn't happen every time ---- that's why I said might ---- but it can happen. And unless there is somebody near by that knows how to override the start in gear protection, it can get expensive.

 

[poconojoe]

All good suggestions. Listen to the experts here. They know what they are talking about. It's run-on or sometimes called pre-ignition. We used to get that more often in our 60's and 70's cars years ago. And with a boat it can be way worse because water will suck into your engine creating hydro-lock which can bend or break things.
Best to try the easy suggestion first. Let the engine idle down after a hard run. Also make sure your idle is not set too high.

 

[poconojoe]

For a variety of reasons, carbon can build up on the top of your pistons. This carbon can heat up so high that it will glow (which acts sort of like a spark plug) and it ignites the fuel air mixture even after you've turned off the engine. This is kind of like how glow plugs work in a diesel engine. And when it ignites prematurely, it causes the engine to rotate backwards.
So this is why it was suggested to check your timing, your fuel/air mixture and make sure you are using fresh fuel of the proper octane for your engine.