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 Post subject: Vapor Lock Conundrum
PostPosted: Fri Aug 21, 2026 8:22 am 
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EFI Slant 6
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Joined: Wed May 28, 2003 9:08 am
Posts: 377
Location: Chelsea, MI
Car Model: 71 Dodge D100 64 Plymouth Valiant Wagon
So I have been suffering from vapor lock--big heat saturation after shutting off the engine. Wrapped fuel line, relocated fuel filter, checked fuel pump. Everything is warm, not hot, to the touch.

What IS hot is the base of my 500 CFM Edelbrock, which is mounted on a Clifton 4BBL aluminum intake. I am not running coolant through the bottom of the intake.
Also added a 1/2" aluminum spacer, and still getting vapor lock.
Intake sits on closed off rear exhaust manifold in Dutra Dual modification.

So Here's The Question:
If I am getting vapor lock without running coolant through the intake, why is the intake heating an option, and if people do use the intake heating, why don't they get vapor lock?

Insights appreciated,
Joe

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Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"


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 Post subject: Re: Vapor Lock Conundrum
PostPosted: Fri Aug 21, 2026 12:39 pm 
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Turbo Slant 6

Joined: Tue Mar 11, 2003 11:47 am
Posts: 671
Location: Illinois
Car Model:
Are you running real 100% gasoline or the almost gasoline stuff that is currently at most pumps in the midwest?

I think the pumps in my locale are currently all 15% alcohol except for a few premium pumps that are either 10% or the single station that has 100% gasoline at 93 octane.

I remember reading vapor lock is worse with higher alcohol contents but I don't know that to be a fact.


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 Post subject: Re: Vapor Lock Conundrum
PostPosted: Fri Aug 21, 2026 1:38 pm 
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Joined: Thu Oct 31, 2002 5:39 pm
Posts: 25012
Location: North America
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A lot of people use "vapour lock" to mean a lot of different hot-fuel-related things. In fact it means only one thing. So let's figure out what's actually happening here. Please describe the symptoms in detail.

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 Post subject: Re: Vapor Lock Conundrum
PostPosted: Fri Aug 21, 2026 1:39 pm 
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Joined: Thu Oct 31, 2002 5:39 pm
Posts: 25012
Location: North America
Car Model:
Quote:
Are you running real 100% gasoline
This is no longer an option for most people in the US and Canada.

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 Post subject: Re: Vapor Lock Conundrum
PostPosted: Fri Aug 21, 2026 3:54 pm 
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EFI Slant 6
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Joined: Wed May 28, 2003 9:08 am
Posts: 377
Location: Chelsea, MI
Car Model: 71 Dodge D100 64 Plymouth Valiant Wagon
Dan--

Good point.

So my symptoms are:
Car runs great
shut down engine for 10-30 minutes
car starts up again fine, but after approx. 5 minutes of driving, loses power. Engine eventually stops.
Rest for 10 minutes, car starts up again, but power loss is quicker.
Last two times I have been able to nurse it home by driving below 35 MPH
Engine temp. gauge reads approx 185--not overheating there.

What I have done to fix the problem:
Changed coil (old coil--Pertronix--felt hot to touch)
re-routed fuel line per article by Dan here on Slantsix.org
used DEI sheathing on fuel line from filter to carb
line is 3/8" injection fuel line
installed 1/2" aluminum spacer under carb
changed to metal fuel filter per article by Dan here on Slantsix.org
checked air filter
ran gas tank down to half full and filled with hopefully higher quality gas

Remaining symptoms:
Fuel line cool
Fuel filter cool
base of 500 CFM Edelbrock carburetor hot.

Next fix:
1/2" phenolic spacer ordered.

I think that's everything.

Still curious about coolant heating Clifford manifold. I had used the heating in the past, but it made the engine run too hot.

Thanks,
Joe

_________________
Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"


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 Post subject: Re: Vapor Lock Conundrum
PostPosted: Sat Aug 22, 2026 5:32 am 
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TBI Slant 6

Joined: Sat Jul 13, 2013 9:17 am
Posts: 130
Location: Denver, CO
Car Model: '70 Barracuda /6 3spd
Quote:
Quote:
Are you running real 100% gasoline
This is no longer an option for most people in the US and Canada.
It's a lot more accessible than you think. A lot of farm equipment doesn't like ethanol, so it's more accessible than folks think

https://www.pure-gas.org/

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 Post subject: Re: Vapor Lock Conundrum
PostPosted: Sat Aug 22, 2026 1:09 pm 
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Board Sponsor & Contributor

Joined: Thu Oct 31, 2002 5:39 pm
Posts: 25012
Location: North America
Car Model:
Aluminum transmits heat very effectively. Ditch the aluminum spacer and replace it by a phenolic one. Add a heat shield, sandwiched with thin gaskets; something like this.

Double-check your float level and your bowl vent adjustments.

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Too many people who were born on third base actually believe they've hit a triple.

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 Post subject: Re: Vapor Lock Conundrum
PostPosted: Sat Aug 22, 2026 1:30 pm 
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EFI Slant 6
User avatar

Joined: Wed May 28, 2003 9:08 am
Posts: 377
Location: Chelsea, MI
Car Model: 71 Dodge D100 64 Plymouth Valiant Wagon
Thanks, Dan.
Your advice is always appreciated.

Joe

_________________
Joe Hoppe

71 D100 225 Super Six 727 AT on 2008 Crown Vic CopCar frame

64 Valiant Wagon 225 904 AT 3:23 8.75"


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 Post subject: Re: Vapor Lock Conundrum
PostPosted: Sat Aug 22, 2026 4:57 pm 
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Board Sponsor & Contributor

Joined: Thu Oct 31, 2002 5:39 pm
Posts: 25012
Location: North America
Car Model:
Gladly. Also pay some attention to what's heating up the engine bay: the exhaust. Things under the hood will cool way down if you'll wrap at least the headpipes and perhaps also the manifolds with this.

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Too many people who were born on third base actually believe they've hit a triple.

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