1968 350 With Edelbrock Carb and Intake Dies Out...

[Loose Screw]

Starts Up nice runs good, but after about 5-10 minutes of driving slow or at idle it starts dying out. this happens warmed up and at about anything around 1.3K rpm or below. If I pick up the rpm to 2-3K it will run good up in higher rpms, but it will start running bad again and die out if I let the rpms go down.
There's lots of gas in the glass filter at the carb and it doesn't blow smoke and I run hot plugs 26s.
I *think the plugs are loading up (I need to read them!)...also some guy told me I need some sort of carb work...I hope it's not that, heck, I Really hope it's not valves or ring work.....

Whatcha Yuh All Think.....Thanks!

[HO455]

Does it do it with the gas cap removed?

What kind of ignition are you running?

[Classics Fan]

It sounds like a carb issue to me, specifically in the idle circuit. I’d start by adjusting the idle mixture. I don’t know Edelbrock carbs but have adjusted and/or rebuilt a few Holleys and a Rochester Quadrajet. There is plenty of info on the internet to get educated on how to work on them. I used to be intimidated by carburetors and working on them but it’s not as difficult as you might think.

[A1971Blazer]

I can't confirm it because I'm a Holley guy, but I've heard that the Edelbrock carburetors don't like more than 5-6 psi of fuel pressure?

[samert111]

Almost sounds like a vacuum leak.

Once warmed up, spray some carb cleaner or brake cleaner around the base of the carb and along the intake manifold where it mounts to the heads. If the engine RPMs flair up then there is a vacuum leak.

[tim_mc]

Originally Posted by A1971Blazer

I can't confirm it because I'm a Holley guy, but I've heard that the Edelbrock carburetors don't like more than 5-6 psi of fuel pressure?

I can attest to this. Edelbrock carbs need a fuel regulator to knock down the pressure to 5-6 psi or they will run very rich.

May not apply, but thought I'd mention it - In addition to fixing the previous rich fuel issue, later on I had similar symptoms where my truck would load up at stoplights during short runs and would have to put it into neutral to keep it from dying. It turned out to be a bad ignition coil on the year-old GM HEI causing weak spark. It would idle fine, but stumbled under a load. Installing a new (and hotter) Davis Unified Ignition coil & module fixed my issue.

Sidebar: The increased dwell in the DUI module made a noticeable difference in throttle response, so I bought one for my brother's '69 Chevelle 396, which woke his car HEI up too. Also fires up instantly all year, no choke.

[Loose Screw]

My brand new mechanical fuel pump is rated at 6.5-8 psi, that's what the spec sheet says. Yeah, there's a lot of pressure there because when I remove the filter that's on the carb side gas flies out of it!
I got points.
I have sprayed carb cleaner everywhere...except right at where the carb mounts to the intake.

The spark plugs I got in there now are only 6 months old. I'm getting ready to read them. I also have a brand new set.

And yeah, there is a lot of pressure when I take the gas cap off.....

Man, I'm just dyin to mess with those (2) brass colored adjustment screw at the front of the carb but I don't even know what they adjust.


Thanks for your help!

[slikside]

Originally Posted by Loose Screw

My brand new mechanical fuel pump is rated at 6.5-8 psi, that's what the spec sheet says. Yeah, there's a lot of pressure there because when I remove the filter that's on the carb side gas flies out of it!
I got points.
I have sprayed carb cleaner everywhere...except right at where the carb mounts to the intake.

The spark plugs I got in there now are only 6 months old. I'm getting ready to read them. I also have a brand new set.

And yeah, there is a lot of pressure when I take the gas cap off.....

Man, I'm just dyin to mess with those (2) brass colored adjustment screw at the front of the carb but I don't even know what they adjust.


Thanks for your help!

One thing at a time.

Start with the fuel psi. It's a well known issue for the Edlebrocks. Just my opinion.

[tim_mc]

The fact that it runs well at first is encouraging. Did you install the Edelbrock carb recently? I run no more than 5 - 5.5 psi of fuel pressure (& have a fuel pressure gauge to watch it). Any more than that will likely cause fuel flooding problems.

As samert111 mentioned, you might want to check the base of the carb for leaks when it warms up to make sure it's got a good seal on the intake.

Speaking of carb seals, I use an Edelbrock 9266 heat insulator gasket to keep the carb from absorbing heat from the intake, otherwise vapor lock/percolating can happen. I highly recommend an insulator gasket if you're currently using a standard one.

You didn't say which model Edelbrock carb you have, but this manual covers most models:
https://edelbrock.com/pub/media/wysi...ers-manual.pdf

The two screws up front are the idle mixture screws, covered on page 6 of the manual.

[Loose Screw]

Okay, so I'm going to get a "Fuel Pressure Gauge" and a "Fuel Pressure Regulator"? I guess from Autozone or Amazon? But first check some YouTubes on the subject. And I will look into this: "Edelbrock 9266 heat insulator gasket". Yeah, and I'm going to have to hunt down what intake and carb I got.

Thanks!

[Loose Screw]

Oh, and my truck came with the Edelbrock carb and intake. It was hacked together and left to sit in the New Mexico Desert for 10 years. it was/is running when I got it about a year ago.....this problem started sometime around the time I switched it from an electric fuel pump to a mechanical one....I know, I know maybe vapor lock. But this problem didn't happen right away, probably like (2) months after I switched it....and I've experienced vapor lock in other vehicles, this probable doesn't seem to *act like Vapor Lock.

[Loose Screw]

Ok, I am studying this, but I'm going to have to ask, what brand & part number fuel regulator and gauge any of you guys using?
I have a mechanical fuel pump with no return port.

Thanks...

[Classics Fan]

Disregard my last post. I just saw your post #11.

[Classics Fan]

Did your problem start when you did something else (like replace the fuel pump) or has it never run well? If I were you I’d do some more troubleshooting before throwing parts at it. Just my $.02.