Max Fuel Pressure for Webers? Is 5psi to much?

[keitho64]

Hello

I am trying to find out what the experts feel is the optimal fuel pressure for Webers. My car is currently running about 5psi and I am going to test a Holley 12-804 regulator that is a 1-4psi regulator and try to dial it close to 3.5. I am thinking 5 is a bit much. Would you all agree?

Background info on the car:

I am getting popping in the exhaust on deceleration and when returning to idle. I have gone through all the valve adjustment, timing, float levels, pump discharge, balance etc. The car runs perfect with only this minor annoyance. It will idle steady at 800, pulls effortlessly to redline, will cruise at 2,500 or 4,000 without skipping a beat.

The car is a mild hot rod 2.7 configured as follows:
34mm venturies
57 Idle jets
145 Main
180 Air Corrector
F3 Tubes
BP7ES Plugs
PermaTune Ignition with Pertronix Ignitor.

Thank you,

[Steve@Rennsport]

Keith,

Webers do not work properly with 5 psi.

We have excellent success with 3.5 psi of regulated fuel pressure.

Remember, float level are totally dependent on this so check them after you make any correction.

[keitho64]

Thank you Steve. I will have the regulator Thursday so I will install and recheck the float levels and rebalance the carbs.

[KTL]

Keith,

Be sure to post your results. My car suffers from a similar problem right now.

[Trackrash]

3.5 psi?

Subscribed.

[RoninLB]

"145 Main
180 Air Corrector
F3 Tubes
BP7ES Plugs"



wild guess

i have my idles turned to give performance when it's running at 3k+ rpm

when turned like this i can run NGK BPR7ES or even BPR8ES

the trade off comes in occasional popping from what i suspect is a lean condition hitting a hot muffler

i can eliminate the muffler popping by turning all the idles rich 1/2 turn and run BPR5ES

i figure it's a simple carb with only 3 circuits etc

[keitho64]

OK here is the latest findings. I installed the Holley regulator and set it to 3.4psi. I rechecked the float level (it was lower than before but I did not raise the float level as it did not seem low enough to warrant changing it) and verified the balance and adjustments as best as I could. The popping has stopped and I am not experiencing the 'rich' smell I used to have. I have not driven the car enough yet to make a final judgment call but I will this weekend. So far preliminary findings are positive.

I will post more results after the weekend drive.

[KTL]

Keith,

Since i've had a similar question & problem, i'll share my findings as well. My questions were answered when } added a second fuel pressure gauge on the regulator's second outlet port. My new Inglese' gauge tells me i'm getting 4psi at the regulator output side. However my mech VDO gauge in the dash reads almost 7!!!

Makes no sense to me that a gauge with a long feed line shows a higher pressure. I would have expected a pressure drop. This suspect gauge makes its tap at a splitter block upstream of the carb inlets, so I don't see why i'm not getting a similar pressure reading since its tapped fairly close to the regulator (where I get the "good" reading from the new gauge)

So I was running very low pressure when I was using the dash gauge to set my system pressure. I dropped the pressure to 4 on the dash gauge, which meant I was getting ~2 or less actual pressure!!! So now I have some confidence in my actual pressure and i'll simply use my dash gauge to confirm I didn't forget to switch on the fuel pumps (racecar has manual toggle for pump turn on)

[KTL]

Keith,

Since i've had a similar question & problem, i'll share my findings as well. My questions were answered when } added a second fuel pressure gauge on the regulator's second outlet port. My new Inglese' gauge tells me i'm getting 4psi at the regulator output side. However my mech VDO gauge in the dash reads almost 7!!!

Makes no sense to me that a gauge with a long feed line shows a higher pressure. I would have expected a pressure drop. This suspect gauge makes its tap at a splitter block upstream of the carb inlets, so I don't see why i'm not getting a similar pressure reading since its tapped fairly close to the regulator (where I get the "good" reading from the new gauge)

So I was running very low pressure when I was using the dash gauge to set my system pressure. I dropped the pressure to 4 on the dash gauge, which meant I was getting ~2 or less actual pressure!!! So now I have some confidence in my actual pressure and i'll simply use my dash gauge to confirm I didn't forget to switch on the fuel pumps (racecar has manual toggle for pump turn on)

[911pcars]

I'd attempt to return the optimistic FP gauge for one that's slightly more accurate. Many gauges are only accurate in the middle of their measuring range. What's the range on your gauge? If it's a manufacturing defect, they should honor it with a replacement.

Sherwood

[JFairman]

If your VDO gauge is a recent one don't trust it. The VDO name looks nice on the instruments in an older German car and thats it.

Current day VDO gauges are some of the lowest quality gauges available.
They have not been made in Germany in a lonnng time.. they are made in third world countries by the lowest bidder, and have been for a while.

[KTL]

Thanks for the tips on the gauge. I don't know the age of it- car came with the gauge already installed. It's a 0-15 psi gauge with mechanical sensing. The Inglese' gaugse is a nice liquid-filled unit that has a 1-6 psi range. So that's right in our target pressure sweet spot and that's why I bought it.

For the VDO dash gauge I have a loooong -4 hose running from the carbs/engine all the way up to the front trunk. I hate having that hose inside the car. Incidentally I also have two other hoses- one main -6 fuel line from the pumps and one -4 for oil pressure.

I can attest to the questionable VDO modern quality. I bought a CHT gauge a while back and the leads are reversed, so it appeared to not work when hooked up. Reverse the leads and it works. Also doesn't "zero" properly when engine is cold.

[Steve@Rennsport]

Originally Posted by KTL

For the VDO dash gauge I have a loooong -4 hose running from the carbs/engine all the way up to the front trunk. I hate having that hose inside the car. Incidentally I also have two other hoses- one main -6 fuel line from the pumps and one -4 for oil pressure.

Holy smokes,....you have fuel lines running inside the passenger compartment to the dashboard??

You're gonna hate me for saying this but thats a very dangerous situation (even if you don't get in an accident). No PCA tech should ever allow that on a track, even for DE.

With all due respect for your well being, I'd kindly suggest (rather strongly) that you install a pressure transducer at the FPR, and use an electric FPR gauge. Its FAR FAR safer and honestly, much more accurate than what you currently have.

[Trackrash]

Steve, maybe he means running through the tunnel?

[RoninLB]

my braided ss fuel lines is plumbed for 3 elec fuel psi gauges and wired to the dash for floating grounds

i've already been on phone with Westach and they'll build just about any psi range i want

[KTL]

That's correct- inside the cockpit = not in tunnel. I have main fuel for engine, oil pressure and fuel pressure. Me no likey.

I did not like that arrangement right from the get-go, but figured i'd reconfigure once I got my fuel system sorted out with a new cell, plumbing, etc. I completely respect what Steve says, however hoses inside the cockpit are treated differently by different sanctioning bodies. Per the NASA CCR:

15.14 Hoses Inside Cockpit
All hoses carrying any liquids or any gases that go through the cockpit must be metal or
steel braided. Any hoses that carry cold water, such as washer fluid, cool suit, etc. are
exempt from this rule.

Coincidentally I just had my car teched for annual race inspection last weekend at my first race event (don't ask how I did.... ) and thought for sure i'd get grilled about the cockpit hoses. But they had no problem with them, despite my distaste for them. If nothing else they're well secured. I understand that means little in terms of safety...

That being said, I completely agree with Steve. I see no reason why the gauges are mechanical. I'd MUCH rather have sheathed wiring running thru my cabin instead of hoses with hot & flammable liquids!!!! The fuel pressure gauge in the dash is going buh bye for sure now that I know it's inaccurate. The replacement will definitely be electronic!

Thanks as always for the feedback and sorry for the hijackification.

[Brandon Mitchel]

Try the 3.5. It fits really good.

[keitho64]

I know this is an old thread but now that the weather is nice again I have another update. With the regulator I did resolve 80% of the issues but it would still act up once in a while. I was as if I was running out of fuel.

My car has the Facet electric fuel pump mounted in the engine compartment and I found out the fuel pressure would intermittently drop. I am planning to move the fuel pump to the front of the car below the tank. I know the pump is good but it loses prime when the tank is low.

I know Porsche put the pump on the 911-T's in the engine compartment, maybe it was not an issue with the 911T motor my 2.7 with Weber's it seems to be.

So the plan next weekend is to relocate the pump and I will report back.

It was a great day today as the weather here FINALLY cleared up and I was able to drive my old friend again.

[Trackrash]

I've had a Facet pump mounted in the engine compartment of my 911 for decades.
Most of my problems ended when I mounted a large fuel filter in line with my Webers.

I have never had a problem with fuel delivery, even to the point of almost collapsing my gas tank on one occasion.

I just finished a day of autocrossing and my carbs never ran out of fuel.

Before you relocate your pump you might want to check for crimped or blocked fuel lines or debris (ie rust) in the gas tank. Also make sure you have an adequate vent on your gas tank.

[1976 TN Porsche]

Try a PMO ( Porsche Mail Order ) Pressure control unit. They work great.