Does this sound like vapor lock?

[JMD]

I have a mild build 454 in my ‘68 k10 that’s fed by a mechanical pump and an edelbrock 800 cfm carb. I also have the original style in-cab fuel tank with a new sending unit/pickup tube. There are two fuel filters in the system, one before and one often the pump and both are clean. The floats are set correctly, and I can’t find any debris in the float bowls.

The truck starts, idles, and drives perfectly. Temp gauge stays right around 200*. However, if I turn the engine off for a few minutes and then try to drive again it falls on its face at anything above 1/2 throttle. Acts like it’s starving for fuel. If I continue to drive it for a few minutes it will clear itself up and won’t have an issue until I shut it down again.

My theory is that while the engine is off and no fuel is flowing, the fuel is boiling between the tank and the pump (the fuel line runs on the inside of the frame and at one point comes within 6” of the passenger side collector). Once the truck runs for a few minutes, the flow of cooler fuel from the tank prevents this from happening and the truck runs fine again.

So do these symptoms point to vapor lock? Or should I be chasing a different problem?

[geezer#99]

Likely the normal fuel boiling in the carb scenario.
You got a heat spacer between the carb and intake?

[rockyrivermark]

Originally Posted by geezer#99

Likely the normal fuel boiling in the carb scenario.
You got a heat spacer between the carb and intake?

Yep. Been there. Especially a prob with eddy carbs.
Get the phenolic spacer. I have a 1”. Solved the prob but 1/2” would likely work also

[JMD]

So the fuel is boiling in the carb? I figured it was boiling in the line because the way the line is routed it comes much closer to heat sources than the carb does.

[rockyrivermark]

Originally Posted by JMD

So the fuel is boiling in the carb? I figured it was boiling in the line because the way the line is routed it comes much closer to heat sources than the carb does.

boiling in the carb. Especially if you have aluminum intake. Carb is sitting directly over the heat source and in direct contact.
Spacers are cheap and simple to install.
Buy one and I’ll bet it solves the issue.

[Greasey Harley]

Before you remove your carb, you could wrap your fuel line with aluminum foil. Just crinkle it around the line, anywhere it's close to a heat source, creating a little heat shield.
I agree that it could well be fuel boiling off in the carb, but I would try this first, because it is quick easy and basically free. It eliminates a variable.

[toolboxchev]

Originally Posted by JMD

So the fuel is boiling in the carb? I figured it was boiling in the line because the way the line is routed it comes much closer to heat sources than the carb does.

Likely preheated by the header, or exhaust manifold collector then boiled in carb, instead of vaporized by intake manifold.

The 1/2 gasket on mine has, I believe, been the primary thing keeping it from vapor locking.

I do also have the stock fan which is always running blowing and cooling the fuel line.

[67bullet]

I had the same problem with my 650 edelbrock avs 2 carb,I installed a 1/4 inch phenolic spacer under the carb.I installed a fuel pressure regulator set to 4.5 psi and problem solved,Edelbrock carbs are well known for this and do not like anything over 5 psi.Hope this helps Jeff

[53burb]

I agree with all of this...back when I had an edelbrock carb, i had same symptom.....i used this.....

https://www.edelbrock.com/heat-insul...hick-9266.html

[rockyrivermark]

$20 spacer and 15 minutes to install.
I’m pretty sure this would take care of it.
Just remember you need a gasket on both sides of the spacer.

[68 P.O.S.]

Originally Posted by rockyrivermark

$20 spacer and 15 minutes to install.
I’m pretty sure this would take care of it.
Just remember you need a gasket on both sides of the spacer.

That Edelbrock spacer WILL solve the percolation issue, however, no additional gaskets are required...this one is designed to go on all by itself. A pressure regulator is a must with Edelbrock carbs to prevent flooding. Edelbrock recommends a regulator set to 5.5psi or their fuel pump that puts out 6psi. It will run great after that...mine does.

[rockyrivermark]

Originally Posted by 68 P.O.S.

That Edelbrock spacer WILL solve the percolation issue, however, no additional gaskets are required...this one is designed to go on all by itself. A pressure regulator is a must with Edelbrock carbs to prevent flooding. Edelbrock recommends a regulator set to 5.5psi or their fuel pump that puts out 6psi. It will run great after that...mine does.

Cool that one has gaskets built in.
My pheilonic didn’t. So just something to keep in mind.
And for sure yes on the fuel pressure advise.

[JMD]

Thanks guys, seems like fairly easy and cheap fix. This may be the push I need to jump to EFI though, it's just one issue after another with this carb. At this point I could have had a Holley EFI system years ago for just few hundred dollars more and it would have saved me a lot headaches.

[geezer#99]

Originally Posted by JMD

At this point I could have had a Holley EFI system years ago for just few hundred dollars more and it would have saved me a lot headaches.

No guarantee with that idea.
I’ve read many threads on several different forums about trading in their carb for efi and never getting them to run right.