Motor keeps running after turning the key off 93 merc carb!

[danadog]

I have put about 50 hrs on the bu this summer and this past weekend the motor did not want to shut off a few times. I would turn the key off and then it would still be chuggin, if I turned the key back on it would run smooth.

What would cause this?

The motor is a 93 carbed merc. No other issues with the motor.

Thanks,

Shawn

[jgouveia3]

this is called "run on" or dieseling, which can happen in carbed motors.

I heard that it is caused because there is carbon built-up somewhere in one or more of the cylinders. The carbon bits, like little glowing coals on the barbecue, retain enough heat to ignite the gas without a spark on the next stroke. The carburetor may keep providing fuel as long as the thing keeps "deiseling."

[JDubya]

Try some fuel system cleaner additive in the tank or carb tb cleaner spray. Jsut don't do this while the engine is running. Follow the directions.

[mike767]

Happened to me when my idle speed was to high. I turned down the idle and the problem went away.

[doughickey]

Another piece of info: If you have an older motor with lots and lots of carbon build-up on the top of the piston, you actualy have increased your compression ratio a bit. (The build-up reduces the volume of space left in the cylinder at the top of the compression stroke.)

Higher compression motors usually need higher octane.

So...... although your engine manual may say you can use 87 octane, you might try 89.

[danadog]

Thanks for the info everyone,

I have been running 85 and that could account for a lagre part of the issue.

Switched to 87 last night and it ran great.

Shawn

[JDubya]

Thanks for the info everyone,

I have been running 85 and that could account for a lagre part of the issue.

Switched to 87 last night and it ran great.

Shawn

85 Really, I don't even think that we can get that down here anywhere.

[danadog]

yep 85 at all the pumps in CO, after running the 87 again last night no issues.

Thanks again

[UWSkier]

Higher elevation gas stops always have lower octane gas. Noticed that out in Wyoming where the highest I could find anywhere was 89 for my sled which normally needs 92-93 here in the lower altitudes.