cant get engine to stop running on???

have a 3.0 L mercruiser and have checked for stray votage in elec system and have adjusted timing and increased octane in fuel, engine will not sut off with key or switch periodically, it wants to keep running on and vibrates the whole boat and shakes erratically,
please help

jake

 

That's called 'dieseling'. Usually caused by deposits in the cylinders or sometimes a bad thermostat. This link describes the problem, and also has links to more detailed sites.

Hope this helps.

 

thanks for the links, i will try to cange the plugs and see if that combined witg cleaning the carb helps. I dont thin my boat has a radiator, but i will check the thermo also, thanks again
jake

 

Sometimes it's as simple as pouring some injector/carb cleaner in the gas tank, too.

 

hey thanks again for the tip, i already used two bottles of that stuff and increased the octane in my fuel, no luck though, i cleaned the plugs and points and i tried to get it time as per instructions in the seloc manual, but it runs even worse now, the timing doesnt advance when i remove the jumper from the dist, all the checks say the distributer is o.k, but the boat runs like crap now. I am gonna try new plugs and wires tomorrow, and any other advice would be greatly appreciated, do you think it could have anything to do with the fuel to air mixture??? and if so, how do i know when its correct???

thanks man, appreciate the help

jake

 

Running on can be caused by an over rich fuel mixture at idle stage.

 

o.k. will try to adjust that, not having much luck with the carb adjustments, but will attempt another try, thanks for the advice
jake