Engine dieseling

[jlr1516]

Any ideas why my L48 350 continues to run (dieseling) after I shut of the engine. Also after I run it for a while the RPM's go way up while in idle. I checked the timing, spark plug gaps, etc and everything seems ok. I haven't messed with any items on the carb it self. I checked the spark plugs and they have alot of carbon on them. I was told that I need to use higher octane fuel?

Since the idle goes up can it be the vacumm advance that might be defective?

Thanks,

Backyard mechanic!!

 

[RevXtreme 1]

Any ideas why my L48 350 continues to run (dieseling) after I shut of the engine. Also after I run it for a while the RPM's go way up while in idle. I checked the timing, spark plug gaps, etc and everything seems ok. I haven't messed with any items on the carb it self. I checked the spark plugs and they have alot of carbon on them. I was told that I need to use higher octane fuel?

Since the idle goes up can it be the vacumm advance that might be defective?

Thanks,

Backyard mechanic!!

A couple of things: The "dieseling" or "run-on" is usually caused by a buildup of carbon and after the car is at operating temp & you shut it off, a glowing piece of carbon can still ignite the mixture under pressure & a cylinder or two will "diesel" and keep the motor turning for a short time. This can be cured by using a higher octain (the higher the octain the less explosive & the more stable a burn so it does not ignite as easily as lower octain), or, do an Seafoam clean to remove some of the deposits. You also probably have the timing bumped a bit to much.

As far as the high idle, sounds like a possible vacume leak... check all vac hoses first, then try spraying brake clean (or carb clean) around the area where the intake manifold joins to the cylinder heads.:thumbsup: