weber...part 1

74er · 07-31-2007, 06:03 PM

Over the winter I've rebuilt a pair of webers and tuned them to some instructions found here. Before I get to the haven't done's yet I would like to know about the fuel pressure. As I was tuning and the car was warming up...yes I know the car is to be warm while tuning...anyways, I noticed the fuel pressure falling off. I have a new CIS pump with the PMO pressure regulator. So I set the pressure at 3.5 psi and as the car warms it falls off. The next day, I start the car and check the pressure. Now the engine and fuel is cold and the pressure reads 6 psi because I kept upping the pressure at it fell during warm up. Are there issues with this or just get the car to operating temp., set the pressure there, and let it be high when cold?

kucharskimb · 07:57 PM

set the pressure without the car running, just fuel pump active, and make sure that the float needle and seats are holding the fuel at 3.5psi. it shouldn't fall off too much with the engine running. this can be your baseline static pressure.

now see where things go after you start it up. probably have to go up on pressure a bit.

i ran into a problem with the PMO regulator/gauge system. the return line to the tank was causing fluctuations. i had to put a restrictor inside the return line, as the little clamp gizmo wasn't restricting enough pressure.. i suppose most folks just don't run a return if they have this problem...

i currently run a holley regulator that controls between 2 - 5 psi before the PMO splitter/gauge.

are you using the plastic insulators? i would recommend them to keep the carbs cooler and avoid vapor lock.

T Bird · 08-01-2007, 04:31 AM

When I switched to Webers, I used the PMO set up together with the MFI fuel pump. After a short while, the MFI fuel pump died. I always suspected that it was the pressure clamp that killed it, since the MFI fuel pump operates at substantially higher pressures than 3.5 lbs. Anyway, I replaced the pump with the OEM Bosch roller cell fuel pump for the Euro 1972 911TV. I believe that it is the same fuel pump used on the 2.2 liter 911T. It is a straight drop in replacement with provision for the return line and it connected right up to the car's existing wiring harness. Since that fuel pump was designed for use with Zeniths and Webers, I tossed out the PMO pressure gauge, which improved the look of the engine compartment. I don't know if this fuel pump is still available, or its cost, but it is, in my opinion, the way to go.

74er · 08-01-2007, 05:10 AM

I'll try the static pressure method which is easy because my '74 pump kicks in with key on and before cranking. Should I do static pressure with engine warm or cold? I have a feeling I'm still going to see a gradual change. Can you expand on the restricter? I didn't receive any clamp gizmo with the kit and from reading PMO's instructions, they indicate to have a free unrestricted pass back to tank which is what I've done. Although I'm thinking a restricter would help. I am using one set of isolators, I believe there are some using two at each bank. I haven't done the drill venting at this point but plan to later.

Mo_Gearhead · 08-01-2007, 05:14 AM

I'm sure the use of Webers / PMOs has created many differing applications that work.

On my restoration (street driven car only, 2.0L) I installed a fuel pump made by NOS for 'motorcycles'. Also used the Holley pressure regulator. Pump is mounted up front near steering, NO return line, regulator in engine compartment set at 4lbs. Pressure very regular/steady. I have only put 300 miles on this car since the rebuild, but no fuel issues.

Just one mans approach.

kucharskimb · 08-07-2007, 01:02 PM

the inline restrictor i made i simply a piece of round 5/16" stock cut to about 1/2" long. I drilled a hole down the centerline with a 1/16" drill. this is placed 3-4" inside the return line (I can still pull it out with a telescoping magnet). the restrictor is held in place with one of the cheap spring type clams that come with replacement fuel filters (the kind you use pliers to remove/install).

This is the first older car that I have had a return line, and I'm still not sure why I hooked it up. i thought maybe it would keep the pump cooler...

I ended up putting a large Carter pump up in my smuggler's box. it's big and heavy, but it's rock steady.

Early 911 Fuel Pumps and Regulators?

azasadny · azasadny's Garage

When Tab Tanner of Autobahn Garage in Findlay, OH converted my '74 over to Webers last December, he replaced my Bosch CIS fuel pump with an aftermarket electric fuel pump that runs at a lower pressure and that setup has been good for me. The fuel pump died in May and the other mechanic who replaced it (Jeff Jones at Automotive Techniques in Novi, MI) also used a high volume, low pressure fuel pump and both guys have said that using the CIS fuel pump is not recommended with Webers or PMO's...

shbop · 08-07-2007, 01:52 PM

ran into a problem with the PMO regulator/gauge system. the return line to the tank was causing fluctuations. i had to put a restrictor inside the return line, as the little clamp gizmo wasn't restricting enough pressure.. i suppose most folks just don't run a return if they have this problem...

I'm also curious if anyone else is having a problem with their PMO regulator. I'm having a fuel supply issue that is leading me back to the regulator. I've noticed my regulator is not that easy to adjust. It takes considerable movement to change psi. Is this a common issue?

JohnJL · 09-08-2007, 04:08 AM

I have a PMO regulator too, thought I find using the static method of testing (ie not monitoring during driving) i am able to adjust pressure from 3.0 to 4.0 with less than 1/4 turn.