Weber fuel system best (design) practices?

[DDS]

Car is 2260cc FAT built, 44IDFs.

Dealing with a few recommissioning issues covered in other threads, and have decided that while I'm at it I should make the fuel delivery system simple, bulletproof and easy to maintain. Thoughts so far:

- Large, easily changed, quality filter installed in the front trunk.

- Fuel pump ideally with integral regulation installed in the front trunk.

- Either a shutoff valve or "pinchable" length of hose in front trunk for service.

- fuel line connected to rigid line at firewall below engine bay, securely clamped - below car, routed through engine bay below firewall, straight through to T fitting at carbs. Well secured, protected from chafe.

Fuel pressure gauge at carbs. (require multi-way fitting)
Rail/tube spanning carbs, secured as appropriate.

I would assume that there should be some flexibility in the lines between the carbs. How can this best be accomplished?

Are banjo fittings at the carbs best or should I fabricate a rigid tube "rail" that could connect to the carbs via stubs of rubber fuel line? (this would also address previous question)

Is there any reason to connect a T (probably with gauge) between the carbs or is it just as well to connect the feed to a T at the first carb, and feed through that there to the second carb?

Is a second, redundant filter advisable near the carbs, or just a nuisance, failure point, and another awkward thing to check?

I have noticed that it is handy to be able to pump some fuel through the system after doing any work, prior to the final reconnection of the carbs in order to flush any accidental contaminants.

I do not currently have a return line. Is there any reason I require one?

Is there really any practical reason to use a lenth of braided line from teh firewall to the carbs, as opposed to high quality, carefully installed rubber line? On one hand, I like the idea of completely failsafe race car/aircraft practices, on the other, ease of repair, maintenance, revision and simple visual inspection is appealing.

Thanks all!

[BoxsterGT]

The factory white nylon feed & return lines in most 914s and 74-75 911s are old & brittle by now and a disaster waiting to happen. If you still have them they should be tossed as soon as possible.

Porsche replaced this nylon fuel tube with black Polyamid tube on all subsequent 911 models and it is still used by Porsche today.

I can make up new Polyamid lines for you to use thru the tunnel with M16x1.5 threads at each end.




Its not expensive and allows you to fit whatever you want for fuel hoses/lines at either end.

Len at Autosportengineering dot com

[Kevin Powers]

why to you want to put the pump and assorted plumbing in the front trunk area?

[Brant]

fuel return is the best way to go

[JmuRiz]

Which of those options do you think is the best for Webers?

Also, what do the shapes stand for? (rectangle, circle, hexagon)

Could I use an FI 2-line fuel line setup so I can run webers or EFI if I wanted?

[Kevin Powers]

large square=fuel tank
smaller rect=fuel filter
sm circle=pump
hex with triangle=fuel pressure reg
large ovals with 3 circles=carbs

[John Rogers]

There are several other ways to connect things and the one most of the southern CA vintage racers use is to have the setup as follows:

tank -> filter -> pump -> large filter -> regulator -> tee -> carb inlets -> loop of fuel line with pressure gauge connecting both carbs. Fuel pressure is generally set to 3.5# at full throttle, higher if you want to rich up the mixture.

The use of the return was stopped back around 2000 or so when some cars burned engines due to the regulator passing too much fuel back to the tank and by the time the drivers noticed it, the engine was shot. This never happened until the races ran on the CA Speedway which has a very long time at full throttle I.E. NASCAR turn 4 to just past NASCAR turn 2 when the infield turn in happens. That also drove everyone to install O2 meters so you could keep an eye on mixture.

[Brant]

John,

that may be the technique used... but its not the ideal technique

a return line allow fuel to flow past the carb inlets (yes the fuel in the bowls is heating) but at least the bowls are being fed a cool fuel supply.

Todays gas are MUCH worse at dealing with heat
fuel lines running through an engine compartment pick up radiant heat
Circulating fuel reduces vapor lock, increases horsepower.

carbs have a needle and seat... they let fuel in when the float opens the needle.
I don't think a poor regulator or anything outside of the carb would change that
Using option B or E would never divert fuel away from the carb inlet path.

recirculatory systems are required on fuel injection engines
They have been used by the factory for years
and are superior

I use option B in the race car and option E in another car.


as a side note..
you do not ever want to mount a fuel gauge on a carb
they vibrate a ton
I have seen the brass fittings crack, I watched a 911 burn at a race track because the gauge was mounted on the carb.

gauges should be mounted on the chassis with a flexible hose/line connecting to the carb

[John Rogers]

Here is a link to a site that explains fuel requirements very well and it does not matter if the car is a drag racer, stock car with a big Holley or one of out vintage race cars with those funky ol Webers, the basic premise is the same. I also have a couple of pics that show the line with fuel gauge that is sitting on the fan shroud connecting both carbs. The idea of vapor lock is true especially if the car is used where it is sitting for periods such as auto crossing or even in heavy traffic on hot days.

A couple of other notes, we always used solid SS 3/4 inch lines through the tunnel and replaced the flex lines in front and on the engine every year as a safety precaution.

Carburetor - Fuel System Tuning

[SirAndy]

Originally Posted by Brant

Using option B or E would never divert fuel away from the carb inlet path.

I tend to agree with this.

Both B and E will keep the bowls full but still circulate the fuel to help keeping things cool.

B would apply to carb fuel pumps with a build in regulator, like most compact rotary pumps.

E would be the same layout as is used on fuel injected systems.

[80-911SC]

I am finishing up getting my parts gathered and looking for a bit of advice ...

So far I have dual 40 webers, a rotary style fuel pump 4-7 psi per the paper, a Holly 1 in two out regulator 1-4 psi , tee w/ fuel gauge 0-15, glass tube style fuel filter and a canister style larger fuel filter

I think I have what I need and thought I had figured it out but now I am rethinking the need to run a return line .... my tunnel appears to have been upgraded to SS lines .. both the large and the smaller ...

The car will mainly be used for AX and weekend running around .. Would E or B be any better ?? the only difference I see is the regulator placement .. .

Also if I have gotten anything wrong in the parts list and you have another recommendations it would be greatly appreciated ...

Thanks
Steve

[Brant]

Originally Posted by 80-911SC

I am finishing up getting my parts gathered and looking for a bit of advice ...

So far I have dual 40 webers, a rotary style fuel pump 4-7 psi per the paper, a Holly 1 in two out regulator 1-4 psi , tee w/ fuel gauge 0-15, glass tube style fuel filter and a canister style larger fuel filter

I think I have what I need and thought I had figured it out but now I am rethinking the need to run a return line .... my tunnel appears to have been upgraded to SS lines .. both the large and the smaller ...

The car will mainly be used for AX and weekend running around .. Would E or B be any better ?? the only difference I see is the regulator placement .. .

Also if I have gotten anything wrong in the parts list and you have another recommendations it would be greatly appreciated ...

Thanks
Steve

I kinda like B
but I don't see any performance difference really between B and E
both move fresh (cold) fuel past the carbs

we put a ton of money and time into our fuel system
its an important system
if your charging system fails you might run the battery low, but if your fuel system fails your race is over or worse something gets damaged or burns

[Brant]

and:

[Brant]

old motor...
but heat shielding all lines: