[Jbetschart]

I went out of town with the boat this weekend and filled up at a Sinclair. A few times when I would shut the engine off it would sputter a little bit before it actually shut down. Doesn't happen every time and I was wondering could this be the gas I filled up with or is there something I can put in the clean it out?

Jeff

[indykoch]

Unfortunately, this is somewhat common on the 3.0 liter 4 cylinder engines, less common on the 4.3 V6, and even less on the V8's. What engine do you have?

I've heard a few things that I'll relay here - this is called dieseling. It is usually due to engine heat that causes the gasoline to ignite even without a spark. I've heard if people run their bilge blower constantly and don't shut off immediately after running fairly hard, that this can be reduced or eliminated.

Somehow, you need to get that heat out. Is your cooling system working properly (fairly new impeller, etc)? Try running the blower more. I've also heard some say a higher octane fuel will help. It requires more heat to ignite, but that gets expensive.

[Jbetschart]

I have a shabah 212Z with the V8 engine.

[SEMIJim]

As indykoch noted: This is referred-to as "dieseling" or "run-on." There are two typical culprits:

• Octane of gasoline too low. Ethanol blends are particularly problematical.
• (Spark) timing advanced too far

That latter one may need some explanation, because one's first reaction tends to be "Why should that matter? The ignition's off." But timing advanced too far causes the engine to run hotter than normal.

First try upping the octane rating of the gasoline you're using. I never buy the lowest-octane fuel for our MerCruiser 4.3L V6. Also recommend you treat your gasoline with Stabil Marine Formula.

Jim

[Jbetschart]

I have been using the Unleaded 85 but will bump it up bnext time I am out and I will also mix in a bottle of the Stabil

[indykoch]

That could very well be the problem - Mercruiser recommends 87 octane. I don't know that I've even seen 85! Where are you located?

[Jbetschart]

Colorado.

I will try the 87 next time and hopefully it fixes the problem.

[SEMIJim]

Originally Posted by Jbetschart

... I will also mix in a bottle of the Stabil

Make sure to get the Marine Formulation. Also you won't mix in an entire bottle. For in-season use, it's only 1 oz. per five gallons of gasoline. I bought the biggest bottle of the stuff they had so it would last a few seasons.

Jim

[Dredd]

Letting it idle for a few seconds before shutting it off should help too.

[ggrims]

I'm on board with everyone that posted. Octane is more important than most think,, It allows a cooler more controlled burn in the cylinder. when the combustion gets hot some edges of parts in the cylinder glow creating the engine to run every time the piston sucks in air/fuel mixture and even though the plug doesnt fire the hot spot will ignite it. Also, make sure the idle is not too high, that can cause the engine to take a few more revs to stop. Good luck,, gremlins on my side are stumping me with my girl.