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Mike Brichta

Best Fix for Dieseling or Engine Run-On?

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After triple checking the engine timing and carb fuel mixture settings I'm still occasionally dealing with engine run-on.  I've read that the best fix for "dieseling" is an electric solenoid in the fuel supply system to instantly stop fuel pressure once the engine is turned off.  I'm not sure exactly what that means or where it goes.

Has anyone dealt with this before and what did you do to fix it?

Thanks!!
Mike

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I was having dieseling problems and I was having my AC repaired so I asked my technician to look at it and I was a combo of Idle mixture and Idle speed. He said my timing was spot on but the car was idling a bit to high. The ac repair had nothing to do with the idle.

Good luck 

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Hey Paul,

I tried that also.  I usually like to keep the curb idle around 800 RPM and even went as low as 600 RPM.  I didn't really change anything other then the idle speed.

Thanks!!
Mike

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I hope you figure it out, maybe some of the others here can give you a hint..

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2 hours ago, Mike Brichta said:

I've read that the best fix for "dieseling" is an electric solenoid in the fuel supply system to instantly stop fuel pressure once the engine is turned off.

This is only for a fuel injected engine. A carburetor draws fuel from the float bowls within, not the fuel line. The fuel pump & line just keeps the carburetor full.

You could get an idle solenoid. It's energized whenever the engine is running and it holds the throttle at your normal idle speed. When you shut the engine, it lets the throttle close further which stops it from running on.

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53 minutes ago, Paul Bell said:

This is only for a fuel injected engine. A carburetor draws fuel from the float bowls within, not the fuel line. The fuel pump & line just keeps the carburetor full.

You could get an idle solenoid. It's energized whenever the engine is running and it holds the throttle at your normal idle speed. When you shut the engine, it lets the throttle close further which stops it from running on.

I think this solenoid was standard equipment on our cars.  If you already have one on yours it may be out of adjustment.

rob

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15 minutes ago, Rob Peters said:

I think this solenoid was standard equipment on our cars.  If you already have one on yours it may be out of adjustment.

rob

That's correct. I think it was a 71 & 72 item.

solonoid.JPG

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Yes I still have the original solenoid but am no longer running a Q-Jet so there is no place to mount it and probably wouldn't line up with the throttle linkage like it did before.

Maybe I should be looking for one for my specific carb?  Sounds like some more research is in my future.

Thanks!!
Mike

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Hey Paul,

I'm running a Demon 1904.  I think the kit I need is a Holley 1950. What do you think?

Can this be used to fix dieseling and as an AC stepup?

Thanks!!

Mike 

 

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Paul, It wasn't only a 71/72 item.  It was on my original 70 350-4brl and is currently on my current 70 350-2brl.  I think my looks a little different than yours but same principal.

rob

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What I'm discovering is that these cars had an idle stop solenoid and no fast idle solenoid.

Demon offers a solenoid, 1950, which you can setup for idle stop for shutdown OR fast idle AC kick up.

I can't find a three position solenoid that does both.

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I'll tell ya what Mike, yank that carb off and upgrade to a Holley Sniper of Fitech Go throttle body EFI and you'll be wondering why you didn't do it sooner. The ONLY difficult part is getting a proper fuel injection fuel supply.

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Mike:

I'm struggling with the same thing on my new (small block) engine build. So far, the only thing that seems to work for me is premium fuel (my compression ratio is 9.6:1) or leaving it in gear (loads the engine) when shutting it off. I'm still breaking it in and fine tuning. I'm optimistic I can solve it without premium fuel.

Like others have said, a fuel shut off/pump won't help, neither will adjusting your timing.

You have a hot spot in the combustion chamber that lights off the remnant fuel/air mix after the key is switched off. Small blocks seem to be more prone to this for some reason. Is this something that just started on an old engine or is this a fresh engine build? 

A few options to try that are simple:

Run some Sea Foam in the gas to try to clean up the carbon deposits in combustion chamber (if an old engine)

Try premium fuel (if a new engine, compression ratio may be a bit higher than you think)

Leave car in gear when shutting it off (this works for me)

If not already, hook your vacuum advance to manifold vacuum, then slow the idle back down (this closes the throttle blades just a smidge more, reducing the air entering the engine at shut down. The same theory as the idle solenoid)

1 step cooler spark plugs

Good luck.

Scott

 

 

 

 

 

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Hey Guys,

Thanks for all of the responses and suggestions.  Here is some additional info on my situation:

- Fairly new GM ZZ4 crate motor (< 2,000 miles) with Hot Cam upgrade kit (400+ HP)
- Already use premium fuel
- I can't turn off while in gear because it is a 4 Speed Muncie (It works if I turn on the AC before shutting off)
- Have already tried adjusting the timing and curb idle screws to no avail
- Already use manifold vacuum

I run a Demon 1904 carb and just ordered the 1950 Demon Throttle Solenoid Kit.  I will be installing it this weekend and will post my results.  Keep your fingers crossed!!

Thanks!!
Mike

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Update:  I installed the Demon 1950 Throttle Solenoid last weekend and set it up so the engine idles around 800 RPM when solenoid is engaged and around 500 RPM when it is not.  That seems to have solved my problem.  Also, the engine starts right up when I go to restart it.  So I guess that was the answer to my problem.

If I ever get the AC working correctly then I may readjust the settings but for now I am happy.

Thanks!!
Mike

 

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How hard was the install? Any pictures?

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Hey Ian,

It was very simple to install the bracket and solenoid.  The kit (1950) was made for my carb (1904) so it fit perfectly.  You will have to run a wire to it which supplies power when the key is turned on.  I tapped off the HEI wire.  I could have also tapped off the electric choke wire as well but the HEI was closer and a thicker gauge wire.

If I get a chance this weekend I will post a pic.

Thanks!!
Mike

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