almost every time i kill the engine to my six it diesels. It does it in cycles really, it get worse and worse until it backfires out of the carb. then for a few days it will be fine. Also before it backfires the engine likes to cut of at idle speed. BTW its a 67' cuda slant six in my 73' valiant.

Here are a few things that work with my wife's scamp.

First off, try some better gas, use a tank of plus or premium every third fill up and you should see a marked improvement.

Carbon buildup or oil deposits are often blamed for this condition. There are some possible ways to reduce buildup and then the higher grade gas won't be required. Do a search.

Good luck!

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1980 Aspen 225 super six

...until you fix it, shut it off in gear - just remember to put it in "park" before walking away

D/W

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If it ain't broke, fix it!

My car diesels as well. It only does it when my engine is really warm and sometimes even then, it doesn't diesel. It's wierd.
Cory

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-'72 Valiant Sedan, Stock (For Now)

I've been round and round with the tuneup on my 72 Dart lately. I rebuilt the carb that had been on there which was running richer all the time. I didn't understand where some of the parts go. Such as the little balls that hit the floor when I took the little metering plate out. There were balls in the kit but I couldn't figure out where they went! So I put it together without the balls. Running quite rich and terrible. I ordered some jets from Jegs and jetted it down and it ran a little better but still a little scary to head to town in. ( By the way why don't 4 barrel jets sizes correlate with slant six jets sizes?) I bought another carb ( a rebuilt ) put it on and it leaked out of the front cover really bad. I started tweaking with that carb then. I machined the cover a little to flatten it for gasket seal and that worked. This latest carb idled good and I expected to be able to drive it all around, but when you mashed down on the gas it would die or nearly die. I went back and forth between these two carb trying to figure out what was going on. Someone on this site I believe mentioned there are balls in the power valve so I put the balls in that kit in the first carb I was trying to rebuild and it runs better now. Although, it diesels when I shut it off if it's warmed up good. So I shut it off in gear most of the time for now. I noticed when I checked compression that I had 150 pounds of cranking pressure which told me I had a little more compression than I thought I had. That was the first time I ever checked it since I built the engine 140,000 miles ago. I don't want to pull the head and grind meat off the pistons or out of the combustion chambers, but that would probably fix the problem. For now I'm thinking of external fixes, such as an air cleaner with air flap which my Dart doesn't have any more. I took it out of the way since it was all frozen up and rusted.

Is the engine running to hot? To you have a working temp gauge?

Check your ignition timing and idle speed. Make sure that your timing is coming back to the proper idle setting (5-10) degrees and that your idle speed is set as low as will promote a smooth idle 550-650 rpm. If those are good make sure you don't have a carb or intake manifold gasket leak.

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"Former Owner" of '65 Barracuda, 225, Auto, MP 2bbl intake, MP cam, Dutra Duals. Presently Moparless.