Stroker engine "diesels" after I shut it down

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I don't buy into "high idle" issue. My car is a stick & idles at 12-1300rpm. No converter to lug it down. True 10.13 to 1, ported iron head & pump gas. Does not "diesel" ever. I do agree it could be something with initial timing or carb not set right. I assume the cam was properly degreed in. That can have drastic affects on performance & idling.
 
Like I said mine idles at 1600 shuts right off in nuetral. Think of what it is doing it is running backward with out the spark plugs firing. That is why it is called dieseling. The fuel is being fired by heat and compression. You won't get rid of the compression which is increased by the motor spinning bacward and you can't stop the fuel. so you got to get rid of the heat from the lean condition. New cars don't have this problem because they are injected and the fuel is shut off

The only thing you can do is cool the charge with more fuel. Sure timing starts the event because of it firing before top dead center. But if it wouldn't be for heat and fuel it wouldn't do it at all . I bet it don't do it cold. Diesels use heat and compression. Then the correct amount of injected fuel at the right time. Increase the fuel it don't start. cut the fuel to shut it down. You cannot cut the fuel with a carb. With diesel there is no ignition No spark plugs involved no timing involved. Where are the spark plugs getting the spark on a car when the key is off. It isfuel and heat from being lean or the exhaust doesn't let the heat out. Those are the two major factors. . Give it more fuel at an idle and it will shut down. Put your hand over the carb just before shutting it off this will increase the fuel. You'll see it will shut off.
 
Timing should be less then 15 degrees advanced at Idle. More will cause a problem.

What kind of problem will it cause?? I run mine at 32 degrees locked at the advice of Brian at Indio Motor Machines and my car starts, runs, and shuts down fine. No problems at all.

I also run my secondaries cracked open allowing me to turn the idle speed down so the primary transfer slots are not over exposed. This was also at the advice of Brian. Car runs great.

Like others have said he should try more initial timing so the idle screw on the carb can be turned down.
 
As far as I'm concerned, if you have an idle of 1300 on a pump fuel street engine, you're not idling any more.
 
As several people have said, idle is too high or the throttle is open too far.

That is why some car companies started to put electrical anti-dieseling throttle stops on the cars.

When ignition was off, the plunger was all the way in and the throttle was totally closed.

When the ignition was turned on, the plunger went out putting the throttle at the idle postion.

So when you turned the engine off, the throttle fully closed and shut off all air getting thru the carb, so any fuel still being sucked thru the jets had no air to combine with.

I don't buy into "high idle" issue. My car is a stick & idles at 12-1300rpm. No converter to lug it down. True 10.13 to 1, ported iron head & pump gas. Does not "diesel" ever. I do agree it could be something with initial timing or carb not set right. I assume the cam was properly degreed in. That can have drastic affects on performance & idling.

All good points made here! I think in addition to a high idle, there has to be a hot spot or hot carbon to act as a glow plug. Also, as Oldmanmopar stated, a lean running, hot engine (with probably a decent amount of carbon buildup) is a perfect storm for dieseling, IMO. A big, fat-running Holley with a polished piston top and combustion chamber edges smoothed, polished and rounded off and little to no carbon build up, yeah....maybe it'll never diesel. If your car is running @ 210+ degrees coolant temp, I'd bet it would even contribute to dieseling. I'll bet you "thinly-veiled race car on the street" guys keep your coolant temps low like 180, right?
 
Mine runs around 180 according to my infrared thermometer and I know I don't run lean but not overly rich either.
 
What kind of problem will it cause?? I run mine at 32 degrees locked at the advice of Brian at Indio Motor Machines and my car starts, runs, and shuts down fine. No problems at all.

I also run my secondaries cracked open allowing me to turn the idle speed down so the primary transfer slots are not over exposed. This was also at the advice of Brian. Car runs great.

Like others have said he should try more initial timing so the idle screw on the carb can be turned down.


As stated I too run a locked distributor. And my idle is over 1500. But having a very large cam with significant over lap. gets rid of alot of cranking pressure at slow speeds which eliminates making heat after coming down to idle. The reason for higher compresion ratios needed for large cams in naturally asperated motors. Timing will not effect motors that don't make alot of pressure at an idle. To diesel you need compression and heat. Advanced timing only starts the reversing in a motor with alot of cranking pressure. Hot spots and a lean condition keep it going. The leaner the mixture the longer it deisels. I have seen some just keep on going and guys just walk away.

At 35 degrees locked a motor will be hard to start without a retard feature or a kill switch to throw on after its already spinning. Or you can just pump the throttle and flood the cylinders to get it to start spinning. My motor is 12.5-1 with a 700 solid roller. I have a 20 degree retard feature and still use my kill switch to start it @ 35 degrees. If not there are times it wants to jam the starter. But it still shuts down warm, Idling @1600 locked at 35 degrees in nuetral it does not diesel. Octane will also help eliminate dieseling.
 
I idn't read all the post's, just going to tell of an experiance I had,
13-1 compression 440 in our pulling truck , ran out of 112 octain fuel while we were putting it in the shop , we put some pump gas in her to get her parked , got her in the shop, turned off the ignition ,DIESEL put her in 1st gear while holding the brake she was spinning the rear tires on idle ( no rear brakes,just front on pulling truck) we finally got her to die by going to a higher gear and letting out on the clutch, never had the diesel with the high octain fuel, Dane

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Really appreciate all the expert ideas here guys! My carb is on a 1" blended phenolic spacer, new gaskets and I do not think anything is warped. This all started after I adjusted the idle up using the primaries so that is where I will start the investigation. Wish my MSD 6AL had start retard though. Lately I have been cranking the engine over with the ignition off to get oil pressure going before it fires as when the engine is cold I have to bring it up to 2000 or so to keep it running until it builds heat. I will also get in the habit of killing the engine in gear with the brake on.

I bought the engine here from a man who had it built 3 years ago and it sat all that time after the dyno runs. I had pulled the heads and took them in to get the valve spring pressures checked. Did not see any spots that could cause hot spots, the heads were pretty nicely prepped and everything was carbon free.

All I know is the dieseling is bad juju not to mention embarassing - just not cool sounding. I even added a little 110 (50%) to the 93 I run and it didn't seem to help so there is something else going on.

And OMM, the X pipe stays. I can't argue with picking up a 10th after adding the X pipe and flowmaster 40's with the associated weight gain. The car sounds pretty good to me inside the un-insulated body but I am told by observers it is a tad loud when stomping it on the street so the 14" x 3" resonators will go on and the ET will determine how it affected the performance. Already bad enough cop bait as the car is still basically a track car with a tag.
 
Have your tried advancing your timing yet so that you can turn the idle adjustment on the carb down to see if that fixed it. Yeah you might have too much total timing so don't wind it up but its a good test.
 
I messed around with the engine last weekend as it was nice and I drove the rod around some. There is not a separete adjustment on the secondaries for the idle opening that I can tell. I backed the timing off a tad. The lighter weight (10W-30) oil really helps the cold natured starting for the first time of the day and the reduced timing also helped stop the diesling and the idle is now around 650-700 in neutral.

Man that car is a blast to drive, especially when manually shifting up and down! I had 8" long 3" dia cherrybombs added in front of the flowmaster 40s and the sound is a lot better. Guys at the local pool bar tell me it sounds like 4 bikes coming in as I downshirt 3-2 and then 2-1 pulling into the parking lot. I explain that at 416 CI it is about 4x the size and the 8 cylinders are 4x more so that sounds about right. The bikers don't like it cause (I think) it makes them think some bikers are pulkling in and they all get up to see who.

Anyways, happy as a clam now. Thanks for all the input FABO.
 
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