96 Mercruiser 4.3L won't cut off when you turn off ignition. Runs good, starts good. What's up?

Question

It keeps "dieseling" so perhaps it is the fuel. We'll try higher octane and see if that helps. It does seem to help if we let it run for a while in idle before cutting it off. We just bought the boat this summer. We'll have it checked if the higher octane doesn't help or even if it does since we'll be taking it out of the water soon. Thanks for your responses.

Answer 1

Not to worry,the base timing is out.and unless you are familiar with engines and setting the timing then I suggest that you take it to a trained tec and have him do it.

Answer 2

Sounds like the ground wire ,usually on top of key switch.running to either coil or ignition module is bad or unhooked. That interrupts the electrical circuit to stop a motor.....George

Answer 3

"won't cut off"?  does it literally keep on running as always or does it do a "dieseling" effect?  if it keeps on as normal, there's a wire loose or a bad ignition switch.  if it "diesels", you need to raise the octane of your fuel.  setting the base timing doesn't necessarily solve this problem.