engin will not shut off

[hl]

While trying to adjust the timing and the carbs on a 1983 90 hp the motor started to rev up and would not shut off after the switch was turned to the off position. Pulling the gas line was how we got it to shut off. We notice the it stopped peeing before it stopped. Any ideas why the motor kelpt running.

 

[CharlieB]

Re: engin will not shut off

Thermal run-away is most likely.

Overheated by the lack of cooling water, the cyl's temp raise to the point the fuel was 'cooking-off' without needing the ignition system.

Shutting off the fuel is the most common method of stopping the motor.

Pull all the spark plugs, inspect all for any 'splashes' of molten aluminum, also rotate the flywheel and look thru each plug hole to see of any piston dome appears very clean, or damaged from any overheating.

Check compression on each to ensure all are relatively the same pressure.

Drop the lower unit and service the water pump, even a few seconds without water at higher RPM can melt the impeller and warp the pump housing.

 

[hl]

Re: engin will not shut off

Thanks, I will check this today

 

[hl]

Re: engin will not shut off

Pulled the plugs; saw no sign of metal and the pistons appeared to be dark colored. Was unable to check the compression. Maybe there was no damage, i hope. By the way , After rebuilding the carbs the instructions said to set the idle mixture 3/4 of a turn from seat position. I always thought it was 1 and 1/2 turns out. Which on is correct?

 

[MercMan82]

Re: engin will not shut off

Whose instructions said 3/4?

 

[hl]

Re: engin will not shut off

The directions that came the the carb kit

 

[CharlieB]

Re: engin will not shut off

Initial idle mixture setting is 1 and 1/2 turns out from 'lightly' seated. This should provide enough fuel to start the motor. Adjust to 'Best' idle speed, 'IN' the water, plus almost another 1/8 turn to provide the additional fuel necessary for crisp acceleration.

If adjusting on the hose, turn @ 1/4 additional open after 'Best' idle, then recheck once on the water and up to temp.


Did you check the black wire w/yellow trace on the ignition switch to ensure it goes to 'ground'' with the key turned OFF?

I may have missed if that was pointed out, the lanyard and ignition switch, both should ground this wire to the solid black wire to kill spark and stop the motor. UN-plugging the main cannon plug or possibly a faulty connection here can also allow a motor to NOT kill. Sliding a small exacto-knife blade down the 'slit' of the male pins will widen them up to make a better connection, just don't over-do it and swell them too fat to go back together.

 

[hl]

Re: engin will not shut off

After checking the plugs and pistons I cranked the motor for a for a minute. It shut off with the switch. I believe the post that said the motor just got too hot. I plan on replacing the water plump and go back to adjusting the carbs. I had the air/mixture out 1 and 1/2 turns as the repair manual said. Just thought I would ask if the the more the needle is turned out the richer the gas mixture becomes.

 

[CharlieB]

Re: engin will not shut off

I had the air/mixture out 1 and 1/2 turns as the repair manual said. Just thought I would ask if the the more the needle is turned out the richer the gas mixture becomes.

That's correct