[John Milner]

What mechanical fuel pump is everyone running with a quadrajet carburetor without running a regulator? I'm running a fuel pump from Napa, part number B0208P, which is a Carter fuel pump. It looks like the pressure rating is 9 pounds. My 17058266 quadrajet doesn't seem to like that much fuel pressure. It starts and idles good cold but when the engine warms up, it will load up at idle. I'm fairly certain that it is the fuel pump putting out too much pressure and overpowering the needle and seat.

[steve25]

9 psi is way too much!

You maybe able to get away with 7lbs, but 6 is safer so it's regulator time for ya!

I once had a Reg go bad and only fed the Q - jet in my street 400 with 3 psi and I only had a slight stumble when on light hills if I kept the rev's below 3000.

If you have the Carb set up with a .136" neddle and seat then the Carb wants volume more then pressure if your motor is making under 550 hp.

Please note that the small Holley Blue regulator has a smaller neddle and seat then if you have a .136" in your Carb so that then is a restriction that you do not want!

[RocktimusPryme]

Ill be the first to kick that dead horse and say that if you ever intend to hit the track for fun, I would take this opportunity to go electric. People told me the same, I didnt listen, and now several years and disappointments later I have an in tank electric pump.

That said, Im a big fan of Robb MC. Both his pump and regulator are top notch, and he is a pleasure to deal with. Very responsive. He offers rebuilds for reasonable prices.

My car never had a problem on the streets with my Robb MC mechanical.

[Skip Fix]

Did you use a gauge to measure the 9 or go by the rating? I've never had any stock type or Carter mechanical pump be a problem for a Q jet or put out 9..

[Formulajones]

I'm still running the same 22 year old stock AC Delco pump on mine lol


That's about to change though if I ever get around to it.

[67drake]

RobbMc 550 with no regulator on my QJ here.

[John Milner]

I have not had a gauge on it yet. I was just going by the rating listed for the pump on their website and by the way the carb acts. Hopefully by the weekend I can put a gauge on it and test it. I have had some good and some bad luck with Airtex pumps with both Quadrajet and tripower carbs. Lately it seems like most Airtex pumps I have bought put out too much fuel pressure. I can't find an AC pump to buy anywhere or I would try one of those.

[steve25]

Why don't you make a call to see the the owners of this site ( Ames) stocks a AC brand pump in the replacements they carry?

[72LuxuryLeMansLa.]

Airtex with the large canister.

[highway star]

Airtex & ACDelco are the same pump. They come in the same box with just different company stickers on the box.
Though there is a price difference.

[68 Firebird]

Been using an Airtex unit with return line with no issues.
Stock pump for a 68 with no AC.

[John Milner]

Well I put a pressure gauge on it tonight and Napa’s website is wrong. It has around 6.5-7 pounds at idle. I guess it is a problem with the Quadrajet.

[77 TRASHCAN]

Test your needle and seat make sure they are not leaking. 6 lbs could still be a tad high.

[389]

Nothing wrong with the Carter fuel pump. I ran two 3/8" lines to mine from my fuel cells sump and that kept that carb full at all times...

[Cliff R]

"Well I put a pressure gauge on it tonight and Napa’s website is wrong. It has around 6.5-7 pounds at idle. I guess it is a problem with the Quadrajet."

I've been running 7.5 PSI fuel pressure on mine with a .145" high flow inlet seat for coming up on 20 years now with zero issues anyplace. It's essentially the same carb you are using, part number 17057274 from a 1977 Pontiac engine. It is set-up with a 140GPH electric pump and has a return to the tank.

The problem is most likely the mechanical pump "pounding' on the seat as the fuel flow stops and starts with each stroke of the pump. Are you using a return to the tank?.....

[Cliff R]

"Well I put a pressure gauge on it tonight and Napa’s website is wrong. It has around 6.5-7 pounds at idle. I guess it is a problem with the Quadrajet."

I've been running 7.5 PSI fuel pressure on mine with a .145" high flow inlet seat for coming up on 20 years now with zero issues anyplace. It's essentially the same carb you are using, part number 17057274 from a 1977 Pontiac engine. It is set-up with a 140GPH electric pump and has a return to the tank.

The problem is most likely the mechanical pump "pounding' on the seat as the fuel flow stops and starts with each stroke of the pump. Are you using a return to the tank?.....

[John Milner]

Originally Posted by Cliff R

"Well I put a pressure gauge on it tonight and Napa’s website is wrong. It has around 6.5-7 pounds at idle. I guess it is a problem with the Quadrajet."

I've been running 7.5 PSI fuel pressure on mine with a .145" high flow inlet seat for coming up on 20 years now with zero issues anyplace. It's essentially the same carb you are using, part number 17057274 from a 1977 Pontiac engine. It is set-up with a 140GPH electric pump and has a return to the tank.

The problem is most likely the mechanical pump "pounding' on the seat as the fuel flow stops and starts with each stroke of the pump. Are you using a return to the tank?.....

I am running a .145 high flow seat. It only starts loading up when it gets warm. It runs and idles great up until then. I am not running a return line to the tank. Do you think it might help if I ran one?

[78w72]

was waiting for cliff to chime in on the psi... he has told me numerous times the later q-jets can easily handle 7psi. & depending on seat size can even go to 8+. i have ran 7-7.5psi with a robbmc 1100 pump dialed all the way down with no regulator with no issues on the street or track as far as idle quality or flooding etc. even tried a regulator & went to 8.5 at the track trying to experiment with solving a fuel starvation issue at the track on low 11sec runs.

another pump to consider for below ~500hp is the edeclbrock pump, it did ok on the street & on the dyno went to about 520hp on a 467 with a SD iron intake & cliffs q-jet but only got into low 12's at the track with much worse starvation. good street pump & into the mid 12's. also it advertises & measured about 6-6.5psi.

[Cliff R]

I had a local customer come in here this morning with his 454 powered 1968 Camaro with an Edelbrock Performer carb on it. His was flooding with anything more than 3psi from his Holley "high performance" mechanical pump purchased from Summit Racing.

I took his carb and put it on the 455 in my Ventura using a 140GPH electric pump at 7.5 psi and it was fine. I even cranked the pressure up to 12 PSI and no issues anyplace.

Put it back on his engine with his "dead-headed" Holley pump and a regulator and it started to flood anything past about 4psi. I would imagine that "dead heading" with a high output mechanical pump may have something to do with these issues.....

[Shiny]

This is a useful thread for me, thanks all.

Long story short, I still need to correct a flooding issue shared a couple years ago. While investigating, I put a pressure gauge on my "dead-headed" fuel line and observed pressure pulses over 7 psi while cranking. I don't know what pump I have but it's aftermarket and a likely suspect.

Here is the video:

Link to Video of Fuel Pressure While Cranking

It may not be my issue but supports and illustrates the possibility Cliff mentions. The average pressure may be fine but if the pump generates intermittent high peak pressure it may overwhelm the inlet valve. There will be a lot of "dynamics" involved with the response of the needle to these pulses but I will check this more when I get back to fixing my car.