Fuel pressure...How much is too much?

[Steveoreno]

I will be using a factory remanufactured 1981-86 Quadrajet (R4-M4ME) on a 1966 327 (slightly warmed over, nothing radical) in my 66 C10. In stock configuration the 1966 327 with a quadrajet ran about 4.5 to 5.5 PSI fuel pressure while in 1981-1986 the pressure was increased to 7.5 to 9 PSI. I have a Carter M6624 fuel pump that pushes 7.5-9PSI. Will this be alright with my setup or should I get a pump in the 4.5-6PSI range? I don't want to overwhelm the carb or engine with fuel pressure. Thanks folks...I appreciate your time and expertise. -Steve-

[MT65]

Fuel pump pressure is not a perfect science, they can and do vary with some of the pumps available, best bet is to get a adjustable regulator. With your setup, 5psi should be sufficient, but I’m sure someone else will chime in…..

[SkinnyG]

It depends on the float size and needle/seat size.

I seem to recall Rochesters need to be on the lower side of pressure (3-5psi).

If the fuel pump keeps the needle and seat open (thus flooding the engine), that's too much.

Try it. Buy a regulator if it needs it.

[Steveoreno]

Thanks guys...you confirmed my suspicions that 7.5 to 9 PSI is a bit much for what I have here. I am just going to go with a Carter M4685 pump...which is pretty much of a stock OEM style pump with 5.5# pressure. I don't really want to get into installing a pressure regulator...I will just shelf the the pump that I have for now. I appreciate it.

[RyanAK]

You might need a regulator anyway. I’m going through this now on my ‘78 K10 Suburban. 350 with Quadrajet. My last two “stock” Carter pumps put out 11-14psi. I want to stay with the stock steel fuel line, but I’m about to swap in rubber hose and a regulator. I’m PO’d.

[Steveoreno]

I don't blame you for being PO'ed Ryan...I would expect better from Carter. It is getting difficult to find AC Delco fuel pumps....feedback from Amazon shows the Delco's to be knock-offs. I'll just hope for the best and go with the Carter. Darn nice looking Suburban you have there!!

[Riverstory]

Originally Posted by RyanAK

You might need a regulator anyway. I’m going through this now on my ‘78 K10 Suburban. 350 with Quadrajet. My last two “stock” Carter pumps put out 11-14psi. I want to stay with the stock steel fuel line, but I’m about to swap in rubber hose and a regulator. I’m PO’d.

Ryan, so I had the same issue. Carb guy (40 yrs in biz) said it was the wrong pump that I kept trying. The pump arm was a different shape and created more pressure based on the stroke of the pump. I ended up getting the correct pump and kept my original metal line from the pump to the carb. I had approx 15psi and ended up with 5.5 psi.

[65truckowner]

I ended up buying a edlebrock fuel pump. They are a little pricy but spot on 5 psi all day long.

[RyanAK]

Originally Posted by Riverstory

Ryan, so I had the same issue. Carb guy (40 yrs in biz) said it was the wrong pump that I kept trying. The pump arm was a different shape and created more pressure based on the stroke of the pump. I ended up getting the correct pump and kept my original metal line from the pump to the carb. I had approx 15psi and ended up with 5.5 psi.

Well that's interesting! What pump did you end up with?

Edlebrock... also a good suggestion.

I had a fuel issue some time ago, eventually chased it to what I thought was a bad pump. Swapped the pump out with a NAPA rated for 5psi. Issue came back. Chased a dozen other things over the course of 6 months. Carb, fuel lines, etc. Eventually, with a gauge plumbed and stuck under the windshield wiper, came back around to fuel pump... fuel pump was dead within a few weeks of installation and then I chased everything else for not. Got a new Carter rated for 5. Got 11. Carb floods on start up. Get another Carter. 14psi. So... time for a regulator.

Or... another new pump.

[The Rocknrod]

I bought one of these, fuel pressure is never high. The only drawback is I replaced it after one year. So this year somewhere in Texas I will be replacing it.
https://www.summitracing.com/parts/TSN-JM1003BK
Back when I had my 53 - five window I installed a Holley Red electric fuel pump. The truck never gave me a bit of trouble for 7 years. It was my only transportation. And I know I didnt install a pressure regulator. V8 SBC,

[Riverstory]

Originally Posted by RyanAK

Well that's interesting! What pump did you end up with?

.

I ended up using an AC Delco 40254. Installed in original 283. Works as advertised for last 2 years.

[The Rocknrod]

The Carter M3120 is rated at 5-6.5 PSI and a flow rate of 30 GPH.