Stroker engine "diesels" after I shut it down

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airwoofer

airwoofer

Drivetrain limit explorer
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It is worse if I idle it then shut it down rather than rev it and shut it off while it is still revving. 10-1, 93 octane, recent build.

I am thinking hot spots but the combustuion chambers looked pretty smooth to me. Spark plug heat range?

Ideas? I know this is not a good thing for the engine.
 
my dads stroker does the same thing, but was told no to be concerned unless it kept running due to fuel n air hitting the hot spots (bad), (and from the engine builder smeddings)

however it does it only everyonce in a while and for less then a second when it does

how long does it diesel after shuttin it down?
 
as others have mentioned it could be a timing issue.....but to step outside the box I will mention a couple other things.

normally when I have had this happen (on any engine for that matter) its a problem with current in the system back feeding. more often than not I find it to be faulty wiring on an electric fan ...as the fan spins after the engine has shut down and back feeds current through the system almost like a generator causing ignition.

if you have an electric fan, try disconnecting it and then starting the car and turning the ignition off and see if the problem still exists.

also if you do not have an e-fan, try disconnecting the alternator wiring and doing the same process as it can cause the same problems some times. After you are able to pin point what is causing the problem,you can then work on the solution.
 
Sounds like either the timing or idle is too high.
 
73AbodEE said:
from my experience.timing.could be wrong.im sure you will get other opinions.
Click to expand...

Agreed, it's usually a sign of the timing having too much initial advance.
 
I'd say idling too high or just a symptom of higher compression. Either way, just shut it off in gear first, then put it in park.
 
whats the initial and total timing set at? They dont need that much total

Is the carb new or rebuilt? could be a circuit leak

check for vacuum leaks yet?

what cam specs? maybe too small for that much squeeze.
 
Why would the timing matter cause the ignition switch is off? I will try shutting off the elec fuel and water pumps before shutting down and see if that helps. My wiring is pretty old and not the best of shape. BTW, idles 850 or so when warmed up. I think the timing is around 34*.

Thanks FABO!
 
TIming is what burns completely or doesnt, and leaves hot spots or doesnt. The run on isnt because of a spark being produced by the ignition. It's usually a hot spot in the cylinder because of retarded timing, combined with a carburetor that's open too far to get a decent idle speed with no timing. There's enough fuel and air drawn in that the engine can "run on" until the hot spot cools and it can't ignite. If you've ever seen "Uncle Buck"... that car has run on....lol.
 
my basic rule of thumb has been pinging=too advanced, dieseling on shutoff= too retarded. There are many other things though as well that can cause it. Bumping the timing up a couple degrees and shutting it back off is a pretty easy test though.
 
Timing should be less then 15 degrees advanced at Idle. More will cause a problem.

If the car has a large cam or larger Cubes. And you have to open the throttle blades past the transfer port because the carb is to small or the idle bleeds are to big. It will run on from to lean. Hitting the throttle will help it cool with a burst of fuel. Holley style carbs whether it be Pro-form , Qick fuel , Barry grant , Or holley. Can be adjusted to correct this.

When you have the carb off without turning the idle screw out the opening of the transfer port should be on covered no taller then it is wide. That will be your highest idle on the primaries for it to transfer properly. If your car will not idle at this position or lower you will need to close up the Idle air bleeds. This makes it suck more fuel at an idle by closing off the air. Think of it as a straw with a hole in it . The bigger the hole the less liquid you'll suck. Close off the hole and you get more fuel at and idle.

I also have strokers . I had a 850 holley on one, A typical double pumper with two corner idle circuit. I had to have the primaries opened up to far just to get it to idle. I couldn't change the air bleeds without drilling and tapping This can be done fairly easy but I wanted a better carb . I bought a 4 corner idle circuit carb and I idle off the secondaries. This leaves the primaries in a position where the transfer ports can work. I lost that little dead spot I had. the carb I bought also has changable air bleeds Idle and Main . They can be change with just taking the Air cleaner off. I decreased the size of the idle air bleeds which added fuel at an idle.

This is what I believe is your problem. Your motor needs more air then the carb can deliver through the primaries. So you need to open them up so far that your out of the idle cicuit. Take your air cleaner off and put you fingers over the outer air bleeds and see what it does. You can control them by sliding your fingers to the side allittle. This will add fuel and correct your running on problem. But the rest I mentioned will help the performance alot.

I had some pics I included which show the air bleeds . These are replacable on these carbs as you can see the screwdrive slot. There are 4 front and rear the outers are the idle.

Also you can see the Idle screw on the frist pic for the secondaries. This is on these carbs just for the reason I explained about the primary transfer. If this wasn't a problem you need to address with big motors with small carbs they wouldn't have these accessable for adjustment. Find someone in your area that really knows there **** on carbs and its an easy fix.

I have tried many carbs on many motors. Holleys, Pro-forms , Demons, Carters, Edlebrocks, BLP's , Grants and the list goes on. The best so far was the Quick-Fuels. They are a bolt on. So far every one I installed . I turned on the pump hit the key and they fired and idled. Very little adjustment needed. Even already rich on idle. They did their homework is my oppinion.

These adjustments mentioned are for holley style carbs only. If you have a Eddy or a Carter Good Luck.. Hope this helps I'm sure there will be those who won't agree . We work on alot of miss matched home built do it there self Cars in our area. When they can't get-em running they usually show up here for my son to fix. Now there could be other things to cover but this would be my first guess without seeing you car. Remember The first thing I mentioned is the Timing. Make sure that the advance is not pulling when at an idle when being shut down. Should be hooked above the venturies if being used. Steve
 

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How big of a stroker? The bigger it is the longer the piston dwells at the top. May have to fatten the jets to cool it off some. Are the pistons quenched properly?
 
You guys are getting pretty technical on me but thanks again!! OMM may be onto the cause... It seems like this started after I opened up the idle (primary side) by adjusting the butterfly stop. I have not touched the mixture adjustments since buying the pro built and dyno'd motor (416). Same MSD mechanical dist as the top picture and the carb looks about the same too. There is a little flat spot just above idle at about 1500 driving with the throttle barely cracked open so OMM may be onto something. The carb is a NASCAR style Holley 830 jetted for the engine on the dyno (unfortunately no temp or density notes). When I first installed the engine I had the timing set (total) at 36* like the dyno run had it. After the over-run pinging I dropped it back a tad which was just after I put on the mufflers / X pipe and thought the increased power (lower ET) was due to less total timing or added backpressure. One day I may have to drop the 750 I have on the 340 on to see how it does as that carb was perfect on the little motor.

As for piston quench - dunno. It has 20cc dished KB forged pistons to get the 10-1. I have to assume that the builder has the quench right as they did a lot of measuring per the build sheet I got.

OMM is that a 4sp or manual VB? I have the kickdown for my 904 and have it set to make pressure when the secondaries start to open. Working pretty well as is the 904 in general when in DRIVE and driving like a cop is behind me. Kicks down nicely when the coast is clear also.
 
Timing using the total method is not the best method for a street driven car.

If that has the 292 nostalgia cam in it, it's gonna need every bit of 15-18 initial. My 2 cents, get the car warm and turn the initial up to 18*, reset idle speed and shut it off. Try to restart it. If it doesn't kick back, see if it shuts down without run on.

Reducing total timing will most likely make the problem worse. Your issue IS NOT a total timing issue, it's an initial timing issue. It will probably take some tweaking of the distributor advance to get it straightened out.
 
to start ,i would simply advance the timing a few degrees and run it. see if that affects it any. if not then move on to your carburetor. and like stated above, if you shut it off in gear, that will prevent any run-on in the mean time. most run-on issues are in the timing.
 
airwoofer said:
Why would the timing matter cause the ignition switch is off? I will try shutting off the elec fuel and water pumps before shutting down and see if that helps. My wiring is pretty old and not the best of shape. BTW, idles 850 or so when warmed up. I think the timing is around 34*.

Thanks FABO!
Click to expand...

Shutting off the fuel pump won't do anything unless it's a fuel-injected engine. You've still got fuel in the bowls. To me, I think the reason retarded initial timing could cause dieseling is because you've got to have the throttle blades cracked open more when the timing is retarded. I'd try to get the idle down as far as I could first, like maybe 750......and as much initial advance as it'll handle.
 
cudavert said:
Shutting off the fuel pump won't do anything unless it's a fuel-injected engine. You've still got fuel in the bowls. To me, I think the reason retarded initial timing could cause dieseling is because you've got to have the throttle blades cracked open more when the timing is retarded. I'd try to get the idle down as far as I could first, like maybe 750......and as much initial advance as it'll handle.
Click to expand...

Yep, that's what Moper, 1wild and I are thinking. There are others that may have mentioned this too. Pretty common issue. The plates being too open continue to introduce fuel to the engine.
 
Had the same problem on another engine and if I left it in drive and held the brake, it would shut off fine....idle was too high so I turned it down and been great since. Idle should be around 800 give or take a bit
 
I will try to use the secondaries for idle as I think this started when I opened it up a little on the primaries to get he idle up a tad. Can use the gear/brake method also. The timing seems pretty good but with so much power how can I tell anyways? I just know that the run-on is bad for the engine and it also makes restarting later harder, instead of an instant HIT it needs to crank. Kinda takes some of the "cool" out of the ride".

Again, thanks FABO!
 
Initial timing affects carb , carb never affects initial timing. Most every carb idle issue I ever come across is not a carb issue at all, it's a timing issue causing the assumed carb problem.

Quick test before you do anything else. Start the car, loosen the dist hold down and turn the distributor body a little bit counterclockwise. If the engine picks up RPM, it wants that additional initial timing or more, now you know what you need to do. If you have a vacuum gauge use it to see how far it wants the initial. I have run in some cases, as much as the starter will handle without kickback.
 
airwoofer said:
You guys are getting pretty technical on me but thanks again!! OMM may be onto the cause... It seems like this started after I opened up the idle (primary side) by adjusting the butterfly stop. I have not touched the mixture adjustments since buying the pro built and dyno'd motor (416). Same MSD mechanical dist as the top picture and the carb looks about the same too. There is a little flat spot just above idle at about 1500 driving with the throttle barely cracked open so OMM may be onto something. The carb is a NASCAR style Holley 830 jetted for the engine on the dyno (unfortunately no temp or density notes). When I first installed the engine I had the timing set (total) at 36* like the dyno run had it. After the over-run pinging I dropped it back a tad which was just after I put on the mufflers / X pipe and thought the increased power (lower ET) was due to less total timing or added backpressure. One day I may have to drop the 750 I have on the 340 on to see how it does as that carb was perfect on the little motor.

As for piston quench - dunno. It has 20cc dished KB forged pistons to get the 10-1. I have to assume that the builder has the quench right as they did a lot of measuring per the build sheet I got.

OMM is that a 4sp or manual VB? I have the kickdown for my 904 and have it set to make pressure when the secondaries start to open. Working pretty well as is the 904 in general when in DRIVE and driving like a cop is behind me. Kicks down nicely when the coast is clear also.
Click to expand...



Well now that I know what you are running I will tell you what I have and why.

The motor is 428 with a solid roller and Indy heads. It is around 12.5 -1 comp. The distribotor is locked a 35 Degrees. It starts at 15 degrees and as the MSD digital 6 automatically retards the timing 20 for start up. When it reaches 800 RPM's it goes to 35 in run mode. So it shuts off at 15 degrees.

The motor idles a 1600 rpms. It has a 5500 stall converter. I shut it off in neutral and I periodically put in pump gas to make it home if I am running low.
If you turn your Idle down on the primaries and turn them up on the secondaries you'll see the dead spot off idle disapear.The proper way of making it real snappy is take the carb off. look at the underside of the carb primaries Open and close the primaries and you'll see the transfer slots. Close them up until as much of what your leaving exposed equals the width of the slot. If you need more throttle than this to make it idle you need to do this with the secondaries. This will let the primaries at the location they need to be for instant throttle responce. They will be able to use the transfer ports for the fuel application transition to the emulsion jets.

Next is the idle air bleeds you want to decrease or increase there size. If you can turn your air mixture screws in almost all the way without stalling you need to decrease the size. This will give you more fuel at idle and the motor will be more responsive with out adding accelarator shot. It will also help the motor to shut down.

I went through exactly what you are discribing. My motor shuts down with no problem now. Get rid of the X pipe , Just my oppinion, They are ok to block up exhausts on teeny motors for more torque. But it will hurt your stroker. Let the exhaust flow. use an H.
 
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.
 
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