18 Ft Chapperall boat keeps going after its turned off?

Question

when you turn the boat off sometimes the engine keeps on going and starts to shake... a mechanic said it might be because of carbon buildup is that true.??

Answer 1

yup, I agree.  if it's running normally with the key off, that's an ignition/wiring/keyswitch issue, but the shake tells you that your cylinders are coked up.

here's a write-up on the "de-carb" process as it relates to outboards, I'm sure you could adapt it for your situation:

http://forums.iboats.com/showthread.php?...

Answer 2

All of these answers are true and may be a symptom of a problem that starts with the regulations for emission standards in California.Mercury and Volvo both have the run-on problem after turning off the ignition.On most engines you could correct it by resetting the timing and adjusting the carb.

I have worked on a few where no matter what you did you could not get rid of the run-on.To fix these,I had to re-jet the carb.Both Mercury and Volvo have service bulletins out about

this problem.I hope this will help you fix your problem.Good luck.

Answer 3

Are you running pump gas from the gas station if so you need to run 87 octane> As marine gas is 87 octane> You can lower the idle> make sure your carb is not leaking gas into the intake>Start running a carbon remover in your fuel> There are some other thing like timing> To high heat rang plugs> engine having a cooling problem> If a closed cooling system 165 to 170 deg Open system is 145 deg> It's not normal for your engine to run on as it's running backwards>Damage can happen> Let idle for a few minutes before shut down>

Answer 4

Yes, excessive carbon buildup can cause the engine to continue even if you shut the ignition off.  This is why people contiously tell people NOT to run any marine engine over 1500 RPM without the exhaust submerged after getting the engine to fully start.  

If that carbon buildup ignites and you have no backpressure on the exhaust provided by water, your engine will overrev and run itself apart into pieces.

Answer 5

Yes, this is probably carbon build-up.  Usually caused by too rich carb settings, excessive idling, poor fuel, or oil  leaking  into the combustion chambers via the valve seals( 4 stroke only).