Hey guys,

I'm curious if I will be able to truly regulate the PSI of say a 255lph fuel pump meant for fuel injection down to the 6psi needed for my carbed motor. This won't hurt the in-tank pump will it?

 

Yes you will need to take your pump out and run either an electric pump mounted on the car somewhere or a mechanical pump. You will burn up your factory pump and it won't suck any fuel out if you switch to a different pump unless you take out your factory pump and replace it some 3/8 fuel line hose.
Mechanical pump is what I went with and it was the easiest in my opinion

 

The car was originally a carbed 305. I don't have a provision for a mechanical pump because the 350 I put in isn't drilled for the pump rod (98 block). I am on my third Holley External Pump (14psi regulated down to 6). They keep burning out because...per what the tech guy at Holley says, they aren't gravity fed. By pulling fuel out the top of my carb pickup (out top of tank), I'm running them to hard and it's burning out the motors.

So I'm stuck with trying an in-tank fuel pump option unless there's another option out there I haven't tried yet.

 

You can regulate it down just fine.

 

I disagree with that. I had a carb on my car at one point and had a holley 255 LPH in tank pump. Using a very high quality pressure reg (aeromotive) I could NOT get the pressure below 8-9 psi using the stock fuel lines. To go much lower I think I would have needed to run a larger return line. At one point, I basically had the regulator adjustment screw backed out to the point it almost fell out. I never saw under 9 psi.

 

Were you able to run effectively @ 9psi? What did you do to fix it? Remember, mechanical isn't an option for me. I may need to upgrade my 5/16 stock retuen line, though I don't know what size the return line is on the EFI sending unit. Isit
5/16 like my carbed one?

 

Put it in perspective. The volume flowing through the return is the same, regardless of the pressure you set the regulator to. If it ran with FI, it will run at lower pressure with a carb.

 

True, but if I have 8-9 psi going to the carb, won't that be too much pressure? I don't want to flood my carb or have gas coming out of the seals.

 

Why are you going to have 8-9 PSI to the carb?

 

I was basing that statement off the previous posters' experience of not being able to get the fuel pressure down below 8-9psi. I don't know yet how well my mallory regulator will work with the new in-tank pump. So I am worried I won't be able to get thepressure down to 6-7psi. I'll find out this weekend when I do the install I guess.

 

I went with an LS1. That was my fix. I did run the carb for a few months with no issues, but a ton of people told me 9 psi is on the high side for a carb application. The seals in them were never meant to handle much psi at all. The stock return line size should be 5/16 on all 3rd gens (which IMO is small anyways- 4th gens are all 3/8).

I'm just giving some insight on my problem. On paper it seems like it should work but that was my true life experience. All set up's/ pressure regs aren't created equal and mine would not go below 9 psi with stock lines and a 255 pump. I heard from a few other guys that a larger return line may be neccesary

 

The key is keeping flow going through the pump. If you can't regulate the output down to 6 psi with a bypass regulator because of the return line size, put another dead-head reg between the bypass reg and the carb inlet, and set it to 6 psi.

 

Where do I check the pressure at then? At the dead head or at the return regulator? I did get a deadhead regulator with my most recent Holly blue pump purchase, came with the pump.

 

At the carb inlet. I'd see if the return type reg controlled it first, then add the deadhead if necessary.

 

Ok. Makes sense.

 

I've used a stock pump and a walbro 340m pump which is 255lph or 67 gpm. Been working for years(8+). I've used the universal aeromotive bypass regulators( comes with an efi and a carb spring). Also used a mallory bypass regulator.

I always ran 6-8psi. Anything over 8 is pushing it. I've seen a lot of floats stuck open.

Also using stock fuel lines. 600hp carb setup.

 

Well, I am only running 325hp at the flywheel and I am hoping that this in-tank pump set up solves my issues. I am worried, as always, about doing something "different" or new to my car that I haven't done before. If I could, I'd just go back to the stock style set up but I can't because the engine has no mechanical fuel pump provision. It gives me hope, hearing from you guys that have done this before and have had success that I will have minimal problems. Then again, I hoped that with my engine swap and dropped probably $3k more than I had budgeted for on that. So I hope this goes...relatively smoothly. Thanks for all the input you guys, I really do appreciate it!

 

So I do have a secondary pusher pump. only 7.5 volts to the harness though so I will have to use my relay that I installed to get the necessary 12v. Damn.

 

Ok, with the regular mallory bypass regulator, I can get it down to 7-7.5psi however fuel starts to seep through the gaskets on the carb.

I installed the second dead-head regulator immediately after the first, actually connected the two with a male-male 3/8NPT fitting. I've got the pressure gauge immediately after the second regulator followed by braided line to the carb. The pressure was nearly at 2psi and I couldn't really regulate it up unless I had the mallory turned almost all the way in (highest pressure setting). I tried adjusting using the dead head but aht didn't move anything. So, I just set the dead head roughly in the middle then used the mallory to set the pressure. Turned almost all the way in I got the pressure after the dead head to rise to 5.5psi and locked it in there. So far no evidence of bleed-through on my gaskets so I think I'm good there.


Now, if I can only figure out why my sending unit is reading passed full.... lol If it's not one thing it's another. Going to have to watch the odometer and get gas every 100 miles until I figure this out. lol