Carb Fuel Pressure

[Roger 911]

I'm in the process of sorting out the Webers on my 2.4 (a 2.4T motor with E cams). The motor seems to run fine at higher revs, but I'm still working on the idle circuit. It seems to run better cold than hot. I have a pressure guage in line after my Facet pump and before my T. When I start the motor cold, I will see about 3.5 psi on the guage. After the motor is hot, I can stop, pop the lid and the guage shows 0 psi. Is this normal? Is the hot fuel in the carbs and/or lines causing the guage to show false readings? Or is my Fuel pump shot? Any help is appreciated.

[Grady Clay]

Roger,

Where is your fuel pump located?

Best,
Grady

[yelcab1]

Draw a picture.
If it is truly 0 psi then you will have severe fuel starvation problem.

[Steve@Rennsport]

Roger:

If I might offer a few suggestions based on a great deal of experience with these things,...

1) You need 3.5 psi for any Weber, PMO, or Zenith carb to function correctly. No more and no less. The float levels should be very precisely set at that fuel pressure.

2) That Facet pump is the biggest POS that there is,..LOL. They are quite unreliable and inconsistent. Plus, they do not deliver the fuel volume you need to keep all four float chambers full at high speed. Get the low-pressure Bosch made specifically for these kinds of applications. Its not cheap, but its VERY durable and long lasting.

[araine901]

The Holly Red will do the trick as well. Steve is right the facit has a very low GPH, it just cant keep up.

[Roger 911]

Steve,
Can I assume that the Bosch pump would also NOT require a pressure regulator? Pelican lists two pumps for carbureted 911s. The cheaper one is shown along with a regulator. I assume the more expensive one is the factory style replacement.

Thanks.
Roger

[B D]

Pelican can also get you the Pierburg pump from PMO. It's a self regulated pump rated at 3.5 lbs. It's quality since PMO uses it and is less than $100 to your door. It's also fairly quiet, quiter than any Facet or Holley.

[project 911]

Roger-

I've just been working on 2.2 with Zeniths today. Facet pump, regulator and pressure gauge. I'm getting similar readings. It will run anywhere from 2 to 4 pounds, but if I rev it hard a couple of times, the gauge drops to zero. I've had 3 gauges on it today, and all three gave different readings, which doesn't help. I'm going to go back to my original pump tomorrow. I don't trust that the Facet is keeping up with the demand.
I hear that the Holley pumps are pretty loud.

[Steve@Rennsport]

Hi Roger:

Carbs can be finicky devices when everything is not perfect.

When these things get well-controlled fuel pressure (3.5), very clean gasoline and are correctly setup, they are VERY reliable. Some pumps produce fuel "pulses" and Weber's-Zenith's- PMO's do NOT like that kind of fuel delivery. Rotary pumps like the Bosch ones provide a constant, steady stream of fuel. Plus, they are very quiet unless they suck air,....

For these reasons, I use an FP regulator in every installation (regardless of pump) along with a high quality fuel filter/water separator. If the floats are spot-on, you never need to fiddle-adjust-tweak them.

I've not touched my Webers since I installed them in 1980.

[Roger 911]

OK. I think I need to pitch the Facet. I just ordered the pump that Pelican lists for 911 w/ Webers '69-'73 @ $116. I don't know if it's a Bosch or Pierburg, I certainly hope it's not another Facet!

On a related note, at least related to Webers, I replaced all the O rings on my mixture screws and idle jets. They were starting to crack and get caught in the threads. I think I removed a little piece from a clogged jet last week, before I realized this was happening.

Eventually, I'm hoping to get the same result as Steve, i.e., adjustment free for 24 years. I should be ready to retire by then, so I'll have more time to fiddle with them anyway!

Thanks for the feedback.
Roger

[Roger 911]

Here's a little update; I installed the new pump from Pelican, an OE Hardi cylindrical type. Whether or not this was needed, it certainly is a much more substantial pump than the Facet type, which does provide some peace of mind. I went for a test drive and it seems to run OK. It definately idles better cold than hot. When it is hot, and idling for a while, it starts to stumble a bit. Would installing insulators between the carb and manifold help this? Any other thoughts on why the idle would deteriorate when hot?

In addition, I have the same readings on my fuel pressure guage now as before, i.e., 3.5-4.0 PSI cold and close to 0 PSI hot. Is this some sort of anomoly with my pressure guage, a Marshal oil filled guage? Is it possible that while the pump is putting out 3-4 PSI on one side of the guage, the hot fuel in the lines (and filters) between the guage and the carbs is expanding to create similar pressure on the other side of the guage. Therefore, due to the design of this guage, it is "netting" to 0. Any other ideas?

Thanks.

[project 911]

Roger-

I'm just swapping out my Facet pump in the next couple days. One thing I did figure out is simple restriction in the system was cutting my pressure down some. Between pump fittings, filters, regulator and "Y" block, there are just too many sharp bends in the system. I took out one filter (it is clean, not plugged), and the regulator and the pressure from my gauge came up about 1 pound from where it was.
When I install my new system, I will use one bigger straight through filter, and try and get rid of some of the 90 degree fittings.

Don't know if that helps you at all...