Ok so i have not gotten to it but i think it is time i raise the question. My 74 360 is acting realy weird after you shut the key off. after you have been runing itt foor a while when the enigne is all hot the idle will start to be higher instead of the very low and speractic at start, well once you go to shut the ke off the engine seems like it want to keep going a very weird like metal bashing sound. imagine like the engine with no spark but trying to run kinda i guess like that but weird has anyone else heard of this or know what to do.???

 

Called dieseling, your idle is too high, either through timing or carb adjustment issues. If it has an auto shut it off in gear, if srt. drv. shut it off, and dump the clutch while holding the brake with it in gear, until you can get it fixed.

It will shut down quickly with a little resistance.




John

 

thanks putting a new carb and intake on it soon so i will adjust it then thanks

 

Deiseling is often caused by too much carbon build-up. Carbon glows red-hot and ignites fuel after igntion is shut off. Run the engine hard for a bit......steep hill and keep the revs up. Might help...........

 

Never heard that one before. Wonder if it works in all parts of the country?




John

 

From Wikipedia:

"Built-up carbon in the ignition chamber can glow red after the engine is off, providing a mechanism for sparking unburnt fuel. Such a thing can happen when the engine runs very rich, depositing unspent fuel and particles on the pistons and valves. Similarly, non-smooth metal regions within the piston chamber can cause this same problem, since they can glow red. It has also been suggested that an improperly rated spark plug can retain heat and cause the same problem."

The whole article is here (incuding your answer as well):

Dieseling - Wikipedia, the free encyclopedia

Seems to me a little kerosene dribbled slowly into the carb when it's idling helps loosen carbon as well...rev it a bit as you dribble it in.

 

9 times out of 10 dieseling is simply the result of having the idle set too high.

 

Well.....I disagree. I agree that lowering the idle will help stop an engine that wants to diesal from doing it, but it's a gasoline engine. It needs soemthing to ignite the fuel. Compression alone won't do it. Glowing carbon deposits will.

In a "good clean" engine, you can set the idle as high as you want, and when you turn off the key, it stops.

A good run to "clean out the carbon" should let you idle high and still shut off properly. A little kerosene usally detonates and also can help to clean out carbon.

However, since I've only eveer had one engine do this, my experience isn't terribly significant to my point of view.

 

so get a quart of kerosene and slowly pour it in the carb wehn running????

 

No...just a few ounces...well.....like 1/2 a pint. You can buy commercial "tune-up-solvent", but reputedly, as most of those "canned" combustion cleaners have a high percentage of kerosene, you can use kerosene only if you already have some. Might save a couple of dollars too!

Best move is a two part effort. First dribble some of the kerosene (or commercial cleaner) into the carb with the engine running. A little tricky as you have to have one hand on the throttle (to keep the engine from stalling) and the other hand slowly pouring in the cleaner/kerosene.

Second effort is the "blow-out" run. Zero to 30 mph at WOT a bunch of times.

It smokes a lot, but after a few runs, and the smoke clears, you're done. If you are also installing new plugs, its probably best to do that after this de-carbonizing effort.

Generally, accumulated combustion deposits are from "Old-Lady-itus" type driving, which is more typical in trucks than cars due to handling and being careful with the load being hauled.

As I mentioned, I've only had one experience with doing this. Seemed to work OK, but it was many years ago and mostly I remember all the smoke...oh yes, and the fear I'd get a back-fire out the carb and have singed eyebrows.

However, I can state that I've had many engines with a high idle that shut down normally when the key was turned off. One example is a freshly rebuilt engine where you idle at 2000 rpm for about 20 minutes to break-in the cam and lifters. Engine always shuts down fine for me after that.

ps: It's very difficult to diagnose over the net, so I may be way out in suggesting all this. However, I'd even go out on a limb and say your that your idle chaning to a higher speed when the engine is hot may even be from those carbon deposits. They fire before the plug does, thereby creating the same effect as advancing the timing.....thus the high idle.

Of course, you may just have a broken vacuum line..........................