Fuel Pressure Issues

[1972BlueC20]

The reason I'm not currently using the Holley 670 carb that came with the engine is because the mechanic who did my engine swap said he couldn't get it running right. He tried to say the carb was defective. I'm not buying that. I might try to put the Holley back on again and see how it runs. I do know first hand it was indeed running bad with the Holley but I think it might have been because I was running a Holley mechanical pump that was putting out about 8 psi and I wasn't running a regulator at that time. Now that I have a Lower psi pump and regulator thats set to 5.5 I think it might act better. I just really like the Edelbrock because they are very good for daily drivers and they seem to get better mpg. I have a # 1406.


As for why I think the fuel is running back down the line it's because after the truck sits and the gauge shows 0 Psi you can take the fuel line off the feed line and nothing comes out but a few drops. If you try that with the pressure still reading it squirts all over the place.

[mechanicalman]

Originally Posted by 1972BlueC20

As for why I think the fuel is running back down the line it's because after the truck sits and the gauge shows 0 Psi you can take the fuel line off the feed line and nothing comes out but a few drops. If you try that with the pressure still reading it squirts all over the place.

Is the choke all the way open when the engine is hot after the fuel pressure goes to zero? Maybe by that time it's started to close and is too rich/hard to start hot.

Mark where you have your choke now so you can go back, but try leaning the choke out a little maybe.

Maybe a phenolic carb base adaptor would help, I suppose it's possible for the fuel in the bowls to be getting too hot but I've stayed away from that because it starts right up cold. I suppose some of it could be vaporizing allowing the float to sink and draining the fuel back into the line and down. This would explain the 0 fuel pressure phenomenon and the vapors maybe flood the engine though vapors usually light off easy.

After engine hot, fuel pressure 0, crank it but not till it starts yet. Remove a plug and see if it's wet.

Something like this with 4 individual holes, and 4 hole gaskets. If you went open adaptor you would lose some responsiveness. Comes with gaskets and studs. I'd go no thicker than 1/2" unless you are sure your cables and linkages will still reach.
http://www.summitracing.com/parts/edl-8723/overview/

[1972BlueC20]

Good points, I'll look into those things!

What's your opinion on plastic phenolic spacers vs the wood fiber one you posted a link to?

[mechanicalman]

Originally Posted by 1972BlueC20

Good points, I'll look into those things!

What's your opinion on plastic phenolic spacers vs the wood fiber one you posted a link to?

I like wood, but only because I like wood and it's small impact on the environment. Not sure if one is better than the other, they all seem to work well on kitchenware.

[mechanicalman]

Originally Posted by 1972BlueC20

The reason I'm not currently using the Holley 670 carb that came with the engine is because the mechanic who did my engine swap said he couldn't get it running right. He tried to say the carb was defective. I'm not buying that. I might try to put the Holley back on again and see how it runs. I do know first hand it was indeed running bad with the Holley but I think it might have been because I was running a Holley mechanical pump that was putting out about 8 psi and I wasn't running a regulator at that time. Now that I have a Lower psi pump and regulator thats set to 5.5 I think it might act better. I just really like the Edelbrock because they are very good for daily drivers and they seem to get better mpg. I have a # 1406.

AVS style Edelbrock Thunder series are the only carbs I like better than the Quadrajets, then AFB style Edelbrock (1406 for example). Quads and Thunders have Adjustable Valve Secondaries, AFB styles can be adjusted but more difficult as you saw in the article you read.

As I remember, you did your homework on the engine installation and you made sure that the shop you used was approved for GM warranty on that engine.

So I'm wondering why the mechanic that said the carb was bad did not contact GM and get you a new one?

You are STILL under warranty. I recommend you take that completely drained carb back to the shop nicely packed in a shipping box ready to go just not taped and request (demand) they file the warranty claim. They WILL be compensated by GM, not only for the carb but for the labor required to install it. They have already done the diagnosis and a carburetor change out, so it's not dis-honest in reality just mis-dated. Tell them "just get me the carb I paid for, make out an R.O. that says you replaced the carb, I'll sign it, don't open the box just give me the carb".

If they insist on actually doing the work, remind them you are not paying ANYTHING and let them install it. I'd prefer the new carb in the box.

Like you, however, I would still prefer the AFB. But it would be nice to have a GOOD 670 Holley carb that YOU PAID FOR. And, what good is a BAD Holley carb? A new one still in the box wrapped with plastic is MUCH easier to sell, or put on the shelf for a rainy day.

BTW, you can go down a little more on fuel pressure if you like, say 5 psi. I've never ran jacked up pressure on an AFB but I tend to believe everybody that says 5.5 psi the max they can stand. I'd stay off the edge, you could play with it by turning it down until it starves for fuel then turn it back up only as far as you need to then another 1/2 lb. (I'm OCD). Yeah, I know, hard to believe LOL