Let's see some suggestions on how to STOP an engine from "dieseling" during shutdown.

[Geoff 2]

I would use the idle sol. You will likely have to fabricate a lever to mount onto the existing throttle lever on the carb. I would also 'design' it so that the t/blades close almost completely [ to remove air flow ] when the key is turned off.

 

[Kern Dog]

I have seen these on smog era carburetors but never thought I'd need one. Here is what I saw in a search using a GM Quadrajet since I remember seeing them:

Note that it is mounted to the side of the carburetor. The one below looks a bit different.

The one above has a more elaborate bracket but seems to achieve the same thing.
The ones below came up in a search at Summit Racing.

This generic one has no mounting bracket but that would be fine since I really doubt that any Holley based carburetor had these things anyway.
The next one looks similar to the first picture:

This last one seems universal/generic:

$140 bucks seems a bit stiff for these things.
So tell me...I'm guessing that the threaded bolt on the end extends when the ignition is ON and retracts with the ignition OFF, right?

 

[Kern Dog]

Here is a Holley bracket but who knows how it mounts or which solenoid it is meant for:

 

[Kern Dog]

Here is the Holley 20-9 bracket.

This looks interesting...

 

[Kern Dog]

The 20-9 bracket:

The solenoid that fits it is the $140 unit:

My carburetor:

Yeah, I need to clean it a bit.

Here are the two tapped holes to mount that 20-9 Holley bracket.

I am lucky that these are available and in stock.

 

[pnora]

The 20-9 bracket:

View attachment 2069221

The solenoid that fits it is the $140 unit:

View attachment 2069222


My carburetor:

View attachment 2069210

Yeah, I need to clean it a bit.

View attachment 2069211

Here are the two tapped holes to mount that 20-9 Holley bracket.

View attachment 2069212

I am lucky that these are available and in stock.

I would use the standard solenoid with the Holley bracket. If you keep looking there are cars that used the bolt on style solenoid instead of the spot weld to bracket style solenoids. You like a project that gives positive results. So pony up the benjamins and go for it.

 

[Mebsuta]

If I have been driving around then shut it off, then spin the engine with a remote starter and the ignition off, it will sputter and try to start, and almost go vrooom. This is with 93 octane E10. I don't know if it's cuz of heat and compression, or somehow residual energy in the ignition (still using breaker points).

Privately, I think it just wants 60s-70s gasoline. idk

 

[Kern Dog]

Finally !
I took the time to test the theory of how the car will respond to a lower idle speed. I went out for a 15 minute drive, peeling out (like men often do) and generally getting everything all warmed up. I was simply recreating the conditions where it will often diesel after I shut it off.
I got back home and turned off the ignition....and it dieseled. I popped the hood, removed the air cleaner and backed off the curb idle screw, watching the throttle back down until the throttle lever bottomed out. I started the car and took it up to the usual 800 RPM idle, then lifted the throttle and shut it down.
Nothing. No dieseling or run on, just silence.
I cranked it up and surprisingly, it idled between 450 and 500 rpms and actually stayed running. I did not press the accelerator pedal, I just let it run, then shut it off.
Nothing. Just silence like you want it to be.
This tells me that the Idle Stop Solenoid would fix this issue. I'll call and order the parts and report back!

 

[WileE]

OR... you could do what I did with my worst car, a /6 Dart back in the 70's = let the car diesel, jump and jiggle, until it stall-farts. Yeah... that car ( actually, just engine ) was a piece of junk.

 

[Kern Dog]

I don't mind if a shitty looking car smokes a bit, has an exhaust leak or diesels sometimes, but.....
The more the car shines, the less tolerant that I am of such things.

 

[66 Sat]

What about leaving the curb idle screw where it is (or just screwing it in a fraction to expose the transfer slots) and then switching to manifold vacuum advance which will bring your idle speed up (and keep it cooler at idle)?

 

[Kern Dog]

I guess that I could try that.
For some reason, I have been hesitant to try manifold vacuum for the distributor.
You know how sometimes you develop a bias for or against something and can't explain why you feel that way?
For me, manifold vacuum is one of those things. I've always used ported vacuum in every car and truck that I have had. Maybe it was Rick Ehrenberg that planted the "ported vacuum" rule into my head.
It is worth a try and it costs nothing.
Thank you.

 

[Geoff 2]

Kern,
I mentioned this waaaaay back in post #45. I suggest you try the simple procedure I outlined. Just plugging in MVA without knowing what the total idle timing will be could introduce other problems & invalidate the test & lead you to think MVA doesn't work....when it does.

 

[Kern Dog]

I tuned out when I read that you mentioned Manifold vacuum. I mentioned why in post #112.
I'm aware that the Idle Stop Solenoid was suggested awhile back. I didn't want to just throw parts at this until I tried a couple of things.

 

[66 Sat]

I guess that I could try that.
For some reason, I have been hesitant to try manifold vacuum for the distributor.
You know how sometimes you develop a bias for or against something and can't explain why you feel that way?
For me, manifold vacuum is one of those things. I've always used ported vacuum in every car and truck that I have had. Maybe it was Rick Ehrenberg that planted the "ported vacuum" rule into my head.
It is worth a try and it costs nothing.
Thank you.

I would connect to manifold vacuum, tweak the idle mixture screws with the vacuum gauge connected and see how you go. One myth with MVA is that the advance drops off right when you need it (on acceleration). It doesn't. It might drop on part throttle, but only to where Ported is rising to.
Example:
With Ported if you have 15° initial + 0° at idle =15° at idle, then part throttle at say 1,500 rpm you have 15° plus 10° Vac advance for a total of 25° at 1,500 rpm on part throttle.

With Manifold you have 15° initial + 15° vacuum = 30° at idle, then part throttle at 1,500 rpm you have 15° plus the same 10° Vac advance for the same total of 25° at 1,500 rpm on part throttle.
It's dropped 5° from idle, but you haven't "lost" anything.

I've been running it for about 3 or 4 years now, no issues. David Freiburger runs his cars on it for what it's worth.

 

[Kern Dog]

You had me until the Freiburger comment....

I watched all of the Roadkill Garage episodes and shook my head at some of the stuff they did. I don't think he is stupid, just that he doesn't build most of his cars to last a long time.
Thank you.

 

[oldbee]

Greg, bring us back up to speed; why is your original idle at 800 anyway? If it ran at 5-600rpm, why not leave it there?

 

[Kern Dog]

I have a manual transmission and the engine is not stock. I don't feel comfortable with having it idle too low with the lope that it has. I was amazed to see that it actually ran at 500 rpms.

 

[toolmanmike]

Greg, bring us back up to speed; why is your original idle at 800 anyway? If it ran at 5-600rpm, why not leave it there?

I have a manual transmission and the engine is not stock. I don't feel comfortable with having it idle too low with the lope that it has. I was amazed to see that it actually ran at 500 rpms.

Does it diesel at 800 but not at 500?

 

[Kern Dog]

Yes. I figured that it is a throttle blade issue. If a solenoid would energize to open the throttle lever once the ignition is ON but then allow it to close further when the ignition is OFF, that seems like a fix for this.
I welcome opposing opinions though since I am not that experienced with this.