# Fuel Pressure Problem?



## 42867Goat (Apr 5, 2011)

Does a mechanical fuel pump normally have low(er) psi at idle? Or is it fairly consistent through all rpm's?

The gauge I have is jumpy, reading from 4-5psi at idle and it smooths out to 4.5psi when I rev the engine. I opened the regulator all the way so it shouldn't be an issue. I'm hoping the pump isn't bad since it is only a year and a half old...

Edelbrock recommends 5.5-6psi for the #1411 carb, and I think the low pressure is the cause of some issues during specific WOT operation. (Merging - WOT through 1st and 2nd, and Idle to WOT from a stop.)

This the pump I put in: Edelbrock 1713 - Edelbrock Performer RPM Street Fuel Pumps - Overview - SummitRacing.com
- This pump would flood the car at idle before I put a regulator on it.


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## geeteeohguy (Feb 2, 2008)

I've always run the stock GM spec mechanical pumps (3-4psi) and have never run it out of fuel...with tripower and wide open. I would think 4.5psi would be more than enough. The jumpiness could be caused by the slower pulses at idle.


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## 42867Goat (Apr 5, 2011)

Well when I hold WOT from a rolling start up an on ramp, at about 4300+ rpm in 2nd it begins to have a huge loss of power and it also does the same from an idling stop to full throttle. If I ease up it stops/doesn't do it.

Sounds like it is out of fuel at these times, but I'm no expert. I suppose the second case could the accelerator pump, but the carb is pretty new and Ive messed with all the settings on the accelerator pump as well as the secondary springs. Although I've tuned it in these areas, it has not eliminated those issues.


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## pontiac (Mar 6, 2011)

not fuel pump, carb jetting and accel pump


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## geeteeohguy (Feb 2, 2008)

I'm with "pontiac"....You are "running out of gas", but it probably is not the pump. I had this same issue and it wasn't the pump...it was a fuel line issue from the tank pickup to the steel line, at the back of the car. I replaced the kinked/rotten hose, and no more "running out of gas" when I kept my foot in it.


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## 42867Goat (Apr 5, 2011)

Alright I think I'll give that a try, but Ill need to get more line, probably won't be until after Christmas.

Thanks, Happy Holidays!


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## billcocarb (Aug 12, 2011)

Don't know if you have a new sender and sock, but had this problem of running out of fuel at higher rpms and found out I had a partially plugged sock filter on the sender, change it out and all was good. Merry Christmas to all.


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## 42867Goat (Apr 5, 2011)

Ill check that too. Thanks I never thought of that, could be as old as everything else as far as I know.


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## geeteeohguy (Feb 2, 2008)

I had the sock fold up on itself when I was driving from CA to Yellowstone back in the late '80's. It would run out of gas, coast the the side of the road, and I would have to get out and get under....and blow the fuel line clear with my mouth. The sock would unfurl like a party favor and be good for another 15 miles, when it was get out, get under, and repeat. It was a loooong way getting home. When I got home, I pulled the tank and cut the sock off. Been running without one for the past 24 years without any ill effects.....


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## 69Goatee (Aug 14, 2009)

:agree with the fuel sock clogged or collasping, it happened to me. Replace the rubber fuel line between the tank and the pump too. The new pump could be pulling the lines closed at high rpm, also happened to me. The Edelbrock has a smaller float bowl and demands a steady fuel supply, you can drain it in a hurry and starve the engine. Yup, it happened to me too.
I wouldn't mess with the jets untill you get the fuel starvation problem solved. The accel pump only helps in the transition from idle to cruise or WOT, and will not cause fuel starvation at WOT.


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## Eric Animal (Oct 28, 2007)

Try it with a full gas tank....might be running out of fuel do to fuel slosh in the tank....thats why guys who drag race and launch hard use sumped or baffled tanks...


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## BearGFR (Aug 25, 2008)

:agree With most of the comments. Your symptoms do sound to me like the motor is "running out of gas" but that can have several causes, such as:
restriction in the fuel supply (dirty filter, dirty "sock', kinked line)
pump "sucking air" (cracked rubber line - or hard line, low fuel level in tank)
carb float level too low
failing fuel pump (or just not up to the task)
fuel line "too small" for engine's needs

Upping the fuel pressure can help to a point but it can also mask other problems. If you get it 'too high' then it'll force the needle off the seat and the fuel bowl will flood/leak everywhere --- not a good thing on a hot engine.

I don't remember seeing information about your engine or how much power you're packing... but if it's significantly "enhanced" over stock it could be the last item - your original 3/8" fuel line just can't deliver enough fuel and needs to be upgraded to 1/2" or larger. Check all the other things first though because they're easier to deal with.

Bear


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## gtojoe68 (Jan 4, 2019)

BearGFR said:


> :agree With most of the comments. Your symptoms do sound to me like the motor is "running out of gas" but that can have several causes, such as:
> restriction in the fuel supply (dirty filter, dirty "sock', kinked line)
> pump "sucking air" (cracked rubber line - or hard line, low fuel level in tank)
> carb float level too low
> ...





BearGFR said:


> :agree With most of the comments. Your symptoms do sound to me like the motor is "running out of gas" but that can have several causes, such as:
> restriction in the fuel supply (dirty filter, dirty "sock', kinked line)
> pump "sucking air" (cracked rubber line - or hard line, low fuel level in tank)
> carb float level too low
> ...


i seem to have the same issue. Have 4 sp 68’ 400 freshly rebuilt, carb rebuilt by pro, new pickup with sock in cleaned tank. Everything is new, except fuel pump. New MSD ignition with box , wires etc. pulls HARD at WOT in 1st up to 5200, I slam into 2nd, pulls right up to 4200 and starts to bog like an old lady. I’ve tuned it, 34 deg advance Ali in at 3000, 1.5 turns out on each mix screw of QJet. Happens even with 3/4 tank gas. Can’t see ignition being issue as it pulls great thru 1st. The fuel lines from tank to mech fuel pump are all original.
Where do I start the witch hunt?! 
Frustrated and at a (power) loss…


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## gtojoe68 (Jan 4, 2019)

gtojoe68 said:


> i seem to have the same issue. Have 4 sp 68’ 400 freshly rebuilt, carb rebuilt by pro, new pickup with sock in cleaned tank. Everything is new, except fuel pump. New MSD ignition with box , wires etc. pulls HARD at WOT in 1st up to 5200, I slam into 2nd, pulls right up to 4200 and starts to bog like an old lady. I’ve tuned it, 34 deg advance Ali in at 3000, 1.5 turns out on each mix screw of QJet. Happens even with 3/4 tank gas. Can’t see ignition being issue as it pulls great thru 1st. The fuel lines from tank to mech fuel pump are all original.
> Where do I start the witch hunt?!
> Frustrated and at a (power) loss…


I went back and re read some old threads, even one I was on (lol). I have some items to check…. Float and fuel running dry in bowl, rubber lines to and from pump, vent line at tank, filter in carb(only one I have) plus probably replace fuel pump that is old anyway. 
thanks


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## BearGFR (Aug 25, 2008)

I had a similar problem with my car that turned out to be a piece of debris in the fuel tank, "Under just the right (wrong) conditions", it would lodge itself into the fuel pickup and almost block it off. 

The way I finally found it was to drop the tank after completely draining it and shake it vigorously. That's when I heard it rattling around. 

Bear


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## RMTZ67 (Mar 12, 2011)

I had been searching for a answer to a bog similar to yours as well gtojoe68. I installed a larger needle and seat, new Carter fuel pump, even tho my other only had 700 miles, fuel filter, raised the float, adjusted the secondaries on my Qjet....all to no avail. Last week I thought I would try advancing my timing a bit more to see if I could get more power out of it. I got more power and my bog, lurching seem to disappear. I could not wait till this weekend to try it again. Just came back from a cruise and all seem well again....Tho I am so used to the bog being there that I am still imagining it there hiding somewhere, only not today. knock on wood, maybe I found my answer.


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## integrity6987 (May 10, 2017)

RMTZ67 said:


> I had been searching for a answer to a bog similar to yours as well gtojoe68. I installed a larger needle and seat, new Carter fuel pump, even tho my other only had 700 miles, fuel filter, raised the float, adjusted the secondaries on my Qjet....all to no avail. Last week I thought I would try advancing my timing a bit more to see if I could get more power out of it. I got more power and my bog, lurching seem to disappear. I could not wait till this weekend to try it again. Just came back from a cruise and all seem well again....Tho I am so used to the bog being there that I am still imagining it there hiding somewhere, only not today. knock on wood, maybe I found my answer.



What fuel are you using and what are the specifics of your ignition set-up and your "new" timing curve?


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## RMTZ67 (Mar 12, 2011)

integrity6987 said:


> What fuel are you using and what are the specifics of your ignition set-up and your "new" timing curve?


I had 12 degree initial, 34 total and all in @ 3000. Bumped it up to 14 and my bog went away. I am at 5000 altitude with 91 octane and 9:6:1 compression. But... while I was messing with that the car got up over 220 degrees but did not spew out. But now I can get it to idle smooth. I checked dwell and was good at 30, Tried adjusting the timing back where it was but did not help the idle, had a new set of plugs lying around so gapped them to 35 but still idles rough.


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## Lemans guy (Oct 14, 2014)

How is your vacumn advance set? Limited to 10 degrees ? Hooked to full manifold vac? And an appropriate vac can that pulls in below idle vacumn? Are you using an adjustable vac can?


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