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 Post subject: 225 Run-On
PostPosted: Mon Aug 21, 2017 3:33 am 
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TBI Slant 6
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Joined: Tue Apr 04, 2017 10:05 am
Posts: 151
Location: Timberlea, Nova Scotia
Car Model*: 1973 Dodge Dart 4-Door Custom Sedan
I'm getting a lot of run-on with my engine when I shut it down and wonder what (If anything) can be done. It's the spare that I'm currently running in my Dart, as the original will be undergoing surgery at the shop this winter. I'm guessing it's carbon buildup in the carb/top of pistons.... maybe.....kinda....

Shawn


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 Post subject:
PostPosted: Mon Aug 21, 2017 6:31 am 
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Turbo EFI
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Joined: Mon May 12, 2008 1:11 am
Posts: 1323
Location: North Georgia
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When mine did that I did the sea foam carbon removal and it made no difference. Turns out my throttle wasn't closing all the way, allowing a little gas to suck past the throttle blade. Check your timing too.

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 Post subject: x2
PostPosted: Mon Aug 21, 2017 8:21 am 
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Board Sponsor
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Joined: Tue Oct 29, 2002 8:27 pm
Posts: 9523
Location: Salem, OR
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Quote:
Turns out my throttle wasn't closing all the way, allowing a little gas to suck past the throttle blade. Check your timing too.


Both of these are the best culprits for this, can also point to a vacuum leak if the carb plates are seated at shutdown...


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 Post subject:
PostPosted: Mon Aug 21, 2017 11:48 am 
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3 Deuce Webber

Joined: Mon Jun 23, 2014 3:13 pm
Posts: 74
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Yes, carbon build up can act as a glow plug and keep things going.
It's called "dieseling".

Also as mentioned, if it can get air, it will automatically draw gas with it.
Although, it still will need a source of "fire" for combustion.
Therefore an air/vacuum leak alone should not result in this situation.

I'm not familiar with your set up, but too much ignition advance can cause this symptem as well.
This is called pre-ignition.

Until you get it sorted out, you can turn it off in gear, with an automatic.
If a standard, you can let the clutch out while standing on the brake to shut it down.


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 Post subject:
PostPosted: Mon Aug 21, 2017 1:43 pm 
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TBI Slant 6
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Joined: Tue Apr 04, 2017 10:05 am
Posts: 151
Location: Timberlea, Nova Scotia
Car Model*: 1973 Dodge Dart 4-Door Custom Sedan
Thanks for the tips! I'll try that turning off in drive one to see if that helps. it's aggravating to have the old girl sputter and cough like an chronic lung patient all the time. lol. Embarrassing as well. All the other Dodges point and laugh.

Thanks again.

Shawn


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 Post subject:
PostPosted: Mon Aug 21, 2017 5:09 pm 
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3 Deuce Webber

Joined: Tue Nov 25, 2014 9:14 pm
Posts: 92
Location: Alberta, Canada
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I wonder if spraying some water into the intake while running might steam clean the carboned cylinders. just pull the air cleaner and mist water over the carb once its warm. same way a coolant leak can show up as a clean cylinder.


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 Post subject: Yep...
PostPosted: Mon Aug 21, 2017 6:06 pm 
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Joined: Tue Oct 29, 2002 8:27 pm
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Location: Salem, OR
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The old water mist down the carb throat to "steam clean" the cylinders is a viable option, but depending on the condition of the engine won't prevent build up after that.... if the deposits are really heavy, the water can frag the carbon and a piece can lodge at the exhaust valve seat and create another issue....

If you decide to do this procedure, warm the engine up... get a spray bottle with water....pull the air cleaner... raise the rpms to a fast idle, spray a mist at the carb airhorn but not continuously.. the carb will want to choke out and engine will want to stall so it's best to spray a little, wait for the rpm to stumble then recover and repeat a few times....depending on the outside temperature you may notice increased water vapor out the tail pipe, and if really bad you may get some black sludge on the ground where the tailpipe outlet is....FYI.


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 Post subject:
PostPosted: Mon Aug 21, 2017 6:15 pm 
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Supercharged

Joined: Thu May 12, 2005 11:50 pm
Posts: 5942
Location: So California
Car Model*: 64 Plymouth Valiant
Get one of those old water injection systems you bought from JC Whitney...........

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 Post subject:
PostPosted: Mon Aug 21, 2017 8:53 pm 
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EFI Slant 6
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Joined: Mon Jan 25, 2010 11:29 pm
Posts: 479
Location: Seattle, WA
Car Model*: 75 Dart SE (2),75 Swinger, 74 Dart Sport,91 Ram RV
We've had 9 Slant-6 Darts & Valients. "Dieselling" has always been an issue with fuel-air mixture ratio and correct initial idle speed setting when trying to shut down a hot engine. "Pre-ignition" (test question in our school) is a pre-mature lighting of the fuel from a HOT SPOT in the cylinder, such as from a chunk of carbon or a feather-edged exhaust valve, or clinker stuck in the firing end of the spark plug. Detonation is from trying to make the fuel do too much work: instead of the fuel burning smoothly in a pattern inside the cylinder, it detonates into an uncontrolled un-even explosion. Detonation is the rattle you hear from the engine when trying to accelerate up a steep hill or when you romp on the throttle going up the highway on-ramp. That is what octane rating is all about: controlling detonation. Both detonation & pre-ignition can trash your pistons etc. pretty fast. (test on Friday, multiple choice. :D :D )

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"Louise", a 1976 Dart Custom project, (now sadly reverted to being just an "organ donor" to our other project Darts.)


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 Post subject:
PostPosted: Mon Aug 21, 2017 10:36 pm 
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Supercharged
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Joined: Sun Nov 03, 2002 9:20 pm
Posts: 12102
Location: Fircrest, WA
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To be honest, in the 20+ years I have been messing around with slant sixes and on the dozens of Mopar vehicles (slant and smallblock powered) I have owned, all with high miles and various states of engine (dis)repair, the only one that has ever had a problem with dieseling is the 76 D100 I currently own. I have a strong suspicion that the wieghts in the distributor are sticking and causing the idle to be far too high which leads to the engine dieseling sometimes when I shut it off.

I would start by inspecting the ignition system, especially the base timing. Verify that he vibration damper still accurately indicated TDC and the base timing is not too far advanced.


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 Post subject:
PostPosted: Tue Aug 22, 2017 4:23 am 
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TBI Slant 6
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Joined: Tue Apr 04, 2017 10:05 am
Posts: 151
Location: Timberlea, Nova Scotia
Car Model*: 1973 Dodge Dart 4-Door Custom Sedan
Gotcha. Thanks! You're right...the idle seems high to me, but we have it adjusted as low as few can, without it stalling. I'll rework it, though
Shawn


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 Post subject:
PostPosted: Tue Aug 22, 2017 4:24 am 
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TBI Slant 6
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Joined: Tue Apr 04, 2017 10:05 am
Posts: 151
Location: Timberlea, Nova Scotia
Car Model*: 1973 Dodge Dart 4-Door Custom Sedan
I tried shutting it off in drive and that seems to alleivate most of the problem.

Cheers,
Shawn


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 Post subject:
PostPosted: Tue Aug 22, 2017 5:04 am 
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Supercharged
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Joined: Sat Feb 16, 2008 1:25 pm
Posts: 5343
Location: Downeast Maine
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Quote:
the idle seems high to me, but we have it adjusted as low as few can, without it stalling


Retarding timing a degree or two, than readjusting idle air/fuel mixture screw will slow idle. On the other hand a vacuum leak can cause high idle.

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 Post subject:
PostPosted: Tue Aug 22, 2017 6:31 am 
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TBI Slant 6
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Joined: Tue Apr 04, 2017 10:05 am
Posts: 151
Location: Timberlea, Nova Scotia
Car Model*: 1973 Dodge Dart 4-Door Custom Sedan
Thanks Wojajr. I'll try that. Shawn


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 Post subject:
PostPosted: Tue Aug 22, 2017 8:34 pm 
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EFI Slant 6
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Joined: Mon Jan 25, 2010 11:29 pm
Posts: 479
Location: Seattle, WA
Car Model*: 75 Dart SE (2),75 Swinger, 74 Dart Sport,91 Ram RV
Intake leak or loose body screws in the carb will make it idle fast too.

_________________
"Louise", a 1976 Dart Custom project, (now sadly reverted to being just an "organ donor" to our other project Darts.)


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