Pontiac Owners Club UK

Does anyone know if the fuel pump off my 4.9 turbo will work ok with a 400 engine or will it pump too much petrol as the turbo engine has a bigger carb and was wondering if it would flood the smaller cfm carb,actually i am not sure what size carb is fitted as its a Holley.The reason i ask is that my turbo pump is brand new and the 400 one has the inlet pipes facing in the wrong direction so the easiest thing would be to fit the turbo pump rather than re routing pipes.


Thanks Jimmy.

most fuel pumps for carbs run at about the same presure, and extra volume wont be a problem, so should be fine

Thanks,i thought it should be ok,i did read that pumps for 2bbl carbs pumped less but the carb i have is a 750 4bbl Holley,so not far off the standard 800 Rochester.

For a carb you'll want to run no more than 6psi, so if the old motor was fuel injected or TBI or if you are in doubt in anyway, get a bypass regulator and set the pressure at 5-6psi. Carbs love volume, hate pressure.

Ozz1967 wrote:For a carb you'll want to run no more than 6psi, so if the old motor was fuel injected or TBI or if you are in doubt in anyway, get a bypass regulator and set the pressure at 5-6psi. Carbs love volume, hate pressure.

Its a 80 4.9 turbo so no fuel injection or electrical gubbins that can go wrong,just straight forward carbs.It worked fine on the 400,just the 400 didn't work fine lol.
When i can start spending again i am gonna rebuild the 4.9T,it will have more poke than the 400 without having to do any expensive mods.

thebandit92 wrote:

Ozz1967 wrote:For a carb you'll want to run no more than 6psi, so if the old motor was fuel injected or TBI or if you are in doubt in anyway, get a bypass regulator and set the pressure at 5-6psi. Carbs love volume, hate pressure.

Its a 80 4.9 turbo so no fuel injection or electrical gubbins that can go wrong,just straight forward carbs.It worked fine on the 400,just the 400 didn't work fine lol.
When i can start spending again i am gonna rebuild the 4.9T,it will have more poke than the 400 without having to do any expensive mods.

Had I thought about it, when I put my 350 together, I would have gone out and found either a pontiac 400 or an older GM 400, or even built the 350 into a 400...then I could put T/A 6.6 on my hood. OOOHHH how awsome would that have been. lol

Hi Guys!

I just read this topic , due to I having problem with my fuel pressure.
The engine revs doesn't really go over 3000, during the the drive if I floor it hardly, feels like it's starving on fuel.The carb is perfect. Yes, the secondary barrels are working fine as well.
That problem is there since I bought it.
The car was a TPI originally, now has a holley carb on it, which is feeded by an electrical fuel pump in the tank.
I guess the fuel filter(-if it has-) getting blocked by dirt,or the fuel pump is too weak.
My problem is:
-I couldn't find filter underneath when the car was lifted up and not even in the engine bay.
-I have not got window cutted in the boot,so I need drop the tank if I wanna go any further.
- I don't understand how the fuel pump pressure was set to the carb in my car.

Ozz 1967 wrote this:
"For a carb you'll want to run no more than 6psi, so if the old motor was fuel injected or TBI or if you are in doubt in anyway, get a bypass regulator and set the pressure at 5-6psi. Carbs love volume, hate pressure."

I thought the same, the carb needs regulated pressure compare with the TPI.
I could not find anything in my fuel line. It's just a pipe, from the tank,without a sign of anyone mess about with it.The return pipe is closed in the engine bay.
?bypass regulator? ?fuel filter?
Where are they ? In the fuel tank?
Where can I get a new pressure regulator if I need one?



Any little help,experience are welcome.

GWD wrote:Hi Guys!

I just read this topic , due to I having problem with my fuel pressure.
The engine revs doesn't really go over 3000, during the the drive if I floor it hardly, feels like it's starving on fuel.The carb is perfect. Yes, the secondary barrels are working fine as well.
That problem is there since I bought it.
The car was a TPI originally, now has a holley carb on it, which is feeded by an electrical fuel pump in the tank.
I guess the fuel filter(-if it has-) getting blocked by dirt,or the fuel pump is too weak.
My problem is:
-I couldn't find filter underneath when the car was lifted up and not even in the engine bay.
-I have not got window cutted in the boot,so I need drop the tank if I wanna go any further.
- I don't understand how the fuel pump pressure was set to the carb in my car.

Ozz 1967 wrote this:
"For a carb you'll want to run no more than 6psi, so if the old motor was fuel injected or TBI or if you are in doubt in anyway, get a bypass regulator and set the pressure at 5-6psi. Carbs love volume, hate pressure."

I thought the same, the carb needs regulated pressure compare with the TPI.
I could not find anything in my fuel line. It's just a pipe, from the tank,without a sign of anyone mess about with it.The return pipe is closed in the engine bay.
?bypass regulator? ?fuel filter?
Where are they ? In the fuel tank?
Where can I get a new pressure regulator if I need one?



Any little help,experience are welcome.

Your best bet will be to find a fuel pressure gauge, and check your fuel pressure. Make sure you're not running more than 6PSI. Did you do the engine swap? Is the return line hooked up?

Hi Mate!
Thank you for answering.

I bought the car with the modifications on.I have no info who did the engine swap.

Yes the return line is blocked.It is ending at the right side of the engine bay,near by the right side exhaust manifold. If I remove the blockage,I can blow it through,even I can suck some petrol from the tank.

Thanks for the fuel-gauge advice, I going for it.

I'm just asking: What is then if I gonna use the gauge and the pressure will be 6PSi,even if I giving some revs? How can I measure it during the drive?
I know : need a long hose into the cabin. . But seriuosly,any better idea?


Last question:
I did know that the ideal pressure of fuel for carbs must be 0.5-0.8BAR (7-11PSI). Is that wrong then?

Additional info:

I can't see any similarish thing in my fuel line like this:
http://www.jegs.com/i/Holley/510/12-803/10002/-1

Check out the web site www.thirdgen.org/techboard

Thousands upon thousands of posts. My name there is the same as here, "ozz1967".

All carbs, should be 4-6psi, anything more than 6PSI and you risk flooding the carb. On mine, when I was setting my pressure initially, fuel spilled out of every oriface on the carb before I brought the pressure down. To check the pressure when running, you need to splice in a gauge. You can buy fittings that you clamp between your hose and carb.

Do you have a fuel pump mounted on the front passenger side of the car? You should not, if the car was originally TPI...

You need to get a mallory 4309 return style fuel regulator. Then get a 3/8 NPT -nipple fitting (For fuel supply), a 3/8" npt - nipple (From regulator to carb), and 3/8" npt to nippple (Fuel return). The Qjets were designed to run with a return line. Tonight, after work, I will take some pictures of my set up and post it for you. For the fuel pressure gauge, you just buy the gauge and there is a spot on the mallory regulator for it. THis way when the car is running, you can always open the hood to check your fuel pressure. Mine is always in place, I never remove it.

Thanks for your reply! It was really helpful!

"Do you have a fuel pump mounted on the front passenger side of the car? You should not, if the car was originally TPI..."
No! I haven't got mechanical fuel pump mounted on the engine. I've got electric fuel pump in the tank.
I have no idea how the electric fuel pump has been set to my Holley,because there's no filter and there's no pressure-regulator in my fuel line.
but I'm sure is not set up properly 'cause my engine is strarving on fuel when it's getting loaded.

...right! The conclusion for me is:
To make it right I've gotta remove the fuel tank,buy a new electric fuel pump,buy fuel-filter with fittings,buy fuel pressure regulator (Mallory 4309 what was mentioned by you or Holley 12-803 what was linked by me above) ,and buy fuel pressure gauge too.
I think that is the way to make it properly ,reliable and powerful.
But I don't know what is gonig to happen with the fuel economy if I get the fuel starvation sorted because it is currently running on ...eh...ahhem..10-17MPG.
Will be hard to be aware of flooring it when you know you've got the power...

Don't rush off and buy a new fuel pump yet! There is no sense in spending 200-gbp if you don't have to. Make sure you're pressure is good/bad and the return system is set up properly first! Also, get the regulator and hook that up before you do anything with the pump. Believe it or not, having that return line hooked up will affect the fuel pressure. The way it's set up now is like a "dead head" set up, basically, the fuel goes to the carb and sits there, creating a low/no pressure area right in front of the carb where it bottlenecks. The return line, basically allows all the excess fuel to return to the tank, thus creating a constant positive pressure flow to the carb. I believe, this is what your problem is.

ONLY, once we've ruled out everything else, should you look at the pump. There are electric pumps out there that are regulated to 7psi internally, it's possible that this is what the previous owner put in (though I wouldn't bank on it).

I will really try hard and get some pictures of my set up today for you to see so you can see how mine is set up.

Close, but not quite.

The fuel feed line gos into the regulator first. From the regulator, one line out to the carb, one line out to the return line. Also, the carb in the picture looks like a Holley, not a Qjet.

"The fuel feed line gos into the regulator first. From the regulator, one line out to the carb, one line out to the return line."

...How on earth could I know? I never had regulator in my car..

"Also, the carb in the picture looks like a Holley, not a Qjet."
I never said I've got Quadrajet,but mentioned many times above I've got Holley,..just look at my signature...

Right!
I gonna measure the pressure first, if it is low then drop tank ,build proper fuel line.
I'm still interesting about yours...so if you've got time to take photos about it then plz.
Anyway thank you for all of the answers.

Wow, for some reason I've been thinking you've had a Qjet all this time. Sorry.

Ok, I'm dumb, I just re-read your first post...says holley, right there. lol

GWD wrote:"The fuel feed line gos into the regulator first. From the regulator, one line out to the carb, one line out to the return line."

...How on earth could I know? I never had regulator in my car..

"Also, the carb in the picture looks like a Holley, not a Qjet."
I never said I've got Quadrajet,but mentioned many times above I've got Holley,..just look at my signature...

Right!
I gonna measure the pressure first, if it is low then drop tank ,build proper fuel line.
I'm still interesting about yours...so if you've got time to take photos about it then plz.
Anyway thank you for all of the answers.

Didn't work out today that I was able to get some pics of it in the light. Tomorrow at work, I"ll go out over lunch and snap some shots with either my phone or camera and post them up.

Ok. Here are some pictures of my regulator. Let me know if you have any questions. Since you have the dual feed carb, you will need to split your fuel line after the regulator, I think, search it over on www.thirdgen.org/techboard to be sure. Again, let me know if you have any questions.

Here is a couple where I'm pointing at my return line. This line comes out of the bottom of the regulator and goes to the return line back to the tank.

Hy!
Sorry mate, I'm in the process of moving house,so I just realized you uploaded your pictures and some description as well.
Thank you for spent your time,it is really helpful,and your previous comments are too.
As I've seen you've got the Mallory regulator fitted.
Also big thumb up for the hose clip that you are using.
I really like those perforated hose clips,especially on small diameter.
They are following the shape of the hose properly compare with a standard one. However they are strong too.
That is the proper way to secure a petrol hose in my opinion .

Because I'm very busy this time ,I haven't got my fuel pressure measured yet,but I think,
I'm gonna be allright to sort the fuel problem out 'cause I've got clue now.
Thank you again!

No worries! Get to it whenyou have time, moving houses is more important! Well...maybe. Depending if you ask me or the wife! Keep at it, I'm sure you'll get it sorted. Let me know if you have any other questions.