Weber fuel recirculation- Questions

[Neilk]

Hi,

In the hot Dallas summers, my Weber'd 911 would occasionally stumble after being stuck at a red light. I think it might have been caused by the heat of the engine possibly causing vapor lock or boiling the gas in the bowls. Several people have mentioned connecting the carbs in line so fresh fuel circulates through them rather than dead ending in each carb. Does anybody have any tips?

What hardware would I need to plumb it? How should I support the fuel line between the carbs. I don't think it should just be laid on top of the engine?

How do I connect the lines to the fuel pressure gauge?

I have attached a picture of what I'd like to do in case my description isn't clear.




Thanks,

[Grady Clay]

Neil,

There are several issues here.
1) Keeping the engine cool.
2) Insulating the carburetors from the heat.
3) Keeping cool fuel to the carburetors.
Possibly more.

Starting with the most important, you can change the fan and crank pulley to give you much more air flow through the engine compartment and critically across the heads and cylinders. Get rid of the heat at the source, everything else is downstream. The set of pieces that turns the fan 1.82:1 is a real bargain.

In ’71 Porsche added a little phenolic spacer (901.108.131.00) between the head and the intake manifold as insulation. You should use one or two of these to keep the heat away from the carburetor. Of course you need longer studs - EZ.

Since your 911S was MFI, you have the return fuel plumbing back to the gas tank. I see the fuel filter and console. My first observation is you have way too many fuel hoses and components in the engine compartment – simplify things. I am a firm believer in circulating fuel systems. There isn’t any firm consensus in the design but this thread may be a good place to gather all the info.

My idea of the reasonable best approach is to have the cool fuel circulate through the carb banjos to a pressure regulating relief valve and then return to the tank. Of course there are many ways to do this.

Best,
Grady

[Steve@Rennsport]

Hi Neil:

What you are asking about has been a VERY common modification to carburetor installations to even out the fuel pressure fluctuations "seen" by each float chamber. This is accomplished on Webers by installing a double-ended banjo fitting to the other two rearward fuel inlets and running a piece of fuel hose between them. Those fittings are now quite difficult to find anymore but this does help and its worth the effort.

I'd also add that you really must have the insulator kit installed between the heads and manifolds to help the prevent heat soak and fuel percolation that is the root cause of your problem.

Needless to say, I've assumed here that your float levels are absolutely PERFECT.

[john walker's workshop]

the PMO float bowl venting tool allows drilling a small vent hole in the carb tops to vent the float bowls of vapors which pressurize the bowls when the fuel percolates. this helps to stop fuel drooling into the throttle bores. PMO also sells the insulator spacer kit with studs and gaskets. in fact, i bet you could get them at pelican.

[Neilk]

Wow, to get answers from 3 EXPERTS, I don’t know what to say besides thanks! So thanks, Grady, Steve and John.

I guess it was a good idea to keep my engine in the garage while the car is being restored 60 miles away. I took some pictures of the carb setup. In the picture below, are those the proper insulating spacers? Should they be thicker?


Can I do the float bowl modification myself or is that only possible with the PMO carbs? My carbs do tend to give off quite an odor in an enclosed garage. Is it the float bowl, bad gaskets or carbs in general? From the picture below, do the carbs look like they need rebuilding or just some tightening of the nuts?


If I get a 1.82 fan pulley, what is the diameter of the pulley so I can go out and find a replacement? As much as I would like a simplified fuel routing, I think I will keep the fuel filter console. The fuel filter seems to work well… I hope.


I should add that the stumbling occurs only occasionally, but it is worrisome when the car stumbles as you are making a left turn against oncoming traffic. It’s so darn hot in Dallas, that I don’t drive the Porsche much in summer, but I would like to prevent it from happening again, especially since the rest of the car will be in top shape. FWIW, I haven’t touched the engine since I pulled it. It will be cleaned before reinstallation.

Thanks again for all your help!

[campbellcj]

FWIW, PMO also sells a solid alloy fuel bar to replace the standard Weber banjo+hose setup; plus they have the correct adapters to "loop" the carbs as Steve describes, using either AN-6 braided or barbed (hose clamp) fittings.

Sorry for the rather poor picture but this gives you an idea how my 914-6 2.2 S-spec is plumbed.

[RoninLB]

I had trouble getting below 5# on a recirculation style plumbing thru the carbs. With a dead head regulator at the loop end, before return, the psi was 6-7#. When I removed the regulator restriction I only got down to 5-6#. I tested a few ga just in case.

My latest bright idea is to T a dead head reg to carbs off a intake-return loop dialed in to 10# with a BP/blow-off style reg.

Below is a pic of bright idea #1 with the loop thru the carbs ending in a dead head reg to return.

[}{arlequin]

ChrisC, can you describe the order in which your fuel is plumbed?

[jpnovak]

Neil, I have the same distrubutor setup in my car.

For the board here is the flow. From the pump the fuel enters the distrubution block. Once there it pressurizes a gauge, splits to each carb and then exits through a return line. I assume the return line is connected to the hardline in the tunnel and then to the tank. This routing is very close to a recirculating system. the only section to dead head is are the two leads from the dist. block to the carb inlet.

Those are the same intake insulator blocks that I have on my car.

Looking at the side of your carbs I suspect a gasket replacement is needed. There is evidence of much fuel weeping from the top plates.

you should also check your float bowls. This may be the cause of your stumble. It may also be that you have a slightly clogged passageway based on the outside crud in the pictures.

OH, I guess you could stop driving where there are stop lights.

[Grady Clay]

Here is my list again from above:
There are several issues here.
1) Keeping the engine cool.
2) Insulating the carburetors from the heat.
3) Keeping cool fuel to the carburetors.
Possibly more.

Just addressing 3), the trick is to have constant fuel flow through the double banjos similar to the flow through the MFI pump. During both idle and peak horsepower some fuel should being returned to the tank, obviously most at idle.

The reason is that when the fuel passes the needle and seat (N&S) in the carburetor, the pressure goes from normal fuel pressure to atmosphere. If the fuel is warm, some flashes into vapor. Each float chamber has a vent up between the stacks to the air cleaner area. That vapor is then cycled back into the intake causing a rich condition.

When the fuel flashes (boils) into vapor there is a cooling effect (heat of vaporization.) On the other side, the vapor can play havoc with proper float level. The N&S likes to meter liquid fuel, not fuel full of vapor bubbles.

The solution is to have an excess of cool fuel circulated past the carb fuel inlets.

There are several satisfactory ways this can be plumbed. I’ll work on describing some designs overnight.


With carbs there is also the issue of heat soak and hot starting.
Early 911 Warm Start Problem


Best,
Grady

[Grady Clay]

OK,

On to Idea #1 system.

Use a rotary type pump, they have less fuel pulsation issues than impulse type pumps. As Tyson suggests, I also like the flow-through CIS rotary fuel pump. It has high volume, the fuel keeps the electric motor cool, proper fittings and if property mounted is quiet.

Put the pump in the front as low as reasonable to the rear of the front suspension cross member. Use rubber vibration mounts. The exact set-up as ’69 E & S and ’70 T, E, & S works great. So do custom installations.

Insulate all the fuel hoses in the transmission area and engine compartment. Aeroquip “Firesleeve” or similar works great.

Since this will obviously be a non-original fuel plumbing, I would recommend using Aeroquip, Russell, etc. metal braded hoses and aluminum fittings. Where necessary, make custom adapters.

Use a metal fuel filter located in the front. I use a CIS filter with custom fittings.

Replace the plastic lines in the tunnel with SS pipes and sliver soldered on fittings. Be sure and use new rubber grommets to support the pipes.

At some point in or near the engine you want to be able to disconnect the two fuel lines for engine removal. Make the two fittings different so they can’t be mis-connected. Make two small hose assemblies (one for the chassis side and one for the engine side) so when the lines are disconnected they can be sealed when the engine is out.

Position the two Tee fittings at the engine so they allow symmetrical L-R flow. Leave a port for fuel pressure measurements and fuel sampling but nothing other than insulated hoses.

Here is the big issue. We need a bypass type fuel pressure regulator. That is one that regulates pressure by passing fuel in order to regulate the pressure on the inlet side of the device. The fuel pump runs at almost maximum flow all the time and the pressure is maintained by the regulator restricting the return flow. I would locate this in the front by the pump and filter.
Summit here lists 93 choices.



The area just aft of the front cross member will be pretty crowded with fuel components. Some careful planning will be necessary to keep everything easily serviceable. Using the aluminum cross member will help as it both gives more room and is easy to mount components to with minimum brackets.

Some of the plumbing rules are:
Have minimum number of fittings.
Minimize bends, particularly sharp angle fittings.
Support hoses and pipes from contact with other parts and prevent chafing.
Never have two angle fittings on the same hose.
Allow for slight extra hose – never have a hose in tension.
Every connection requires two wrenches.
Never plumb a mechanical fuel pressure gauge into the cockpit, there are good electrics.


What I have described is a complete make-over of the fuel system. It accomplishes several things:
1) It is a totally metal encased and fitting sealed system. If properly done, it should be safer and outlast the Factory system.
2) It is serviceable.
3) It fulfills the goal of keeping cool fuel at the inlets to the N&Ss.
4) It solves some of the dreaded vapor lock issues by minimizing components in the hot engine/transmission area.
5) It moves some weight forward and down low.

An important extension might be a solenoid valve that is normally open (12 volts closes the valve) parallel to the pressure regulator. When the car is off this bleeds pressure back to the tank. Any fuel boiling during heat soak doesn’t generate any pressure and possibly flood the carbs.
With the right bypass pressure regulator it could have an extra bypass with just a restrictor.

A very important “while you are there” is a Haylon fire suppression system.


Here are some good links that Dave posted:
“here's one of 'em:
http://forums.pelicanparts.com/show...light=3.0+carbs
Here's Tyson's recirculating suggestion:
http://forums.pelicanparts.com/show...ng&pagenumber=1
Ron's set up:
http://forums.pelicanparts.com/show...&highlight=feed
Here's a good link from John C's post:
http://www.centuryperformance.com/fuel.asp

Ronin did a nice job of implementing Tyson’s suggestions.
I would like to see less fuel components and extras in the engine compartment and cover the hoses with Firesleeve.

What did Chuck Moreland end up with?

Whatever someone does, properly document what you have done. Keep a file of all the components, hoses, and custom pieces.

Best,
Grady

PS, I’ll work on a diagram.

[}{arlequin]

Grady,
Thanks again for a wealth of info and good answers. A diagram would go a long way (at least for me) to help visualize the setup.

If I'm switching from CIS to this type of system, am I completely ditching the accumulator?

[RoninLB]

Originally posted by Grady Clay
Ronin did a nice job of implementing Tyson’s suggestions.
I would like to see less fuel components and extras in the engine compartment and cover the hoses with Firesleeve.

my problem became the return restriction seeking carb 3.5psi. So either my stock pump is very high volume or I have a return line flow problem. My first thought was a new return pipe or an 8AN high end hose. No guarantee that that'll work, and I really didn't have my head up for that so I drifted into another design which actually gives the dead head good fuel availability. The dead head Holley will have great fuel supply close by of 10psi consistantly from the Mallory by-pass/ blow-off/ back presure regulator. whatever.


The by-pass/ BP regulator would be safer up front. The dead head could leak so another possible leak from the by-pass reg is part of the program. I never thought about a carb fuel psi bleed off. Just what I need is more plumbing, lol. Anyway if bright idea #4 is not acceptable I can always do bright idea #5.

A fume sniffer is a requirement on any dead head reg to carbs imo. An on-board fire control system will have to wait.

fwiw, I like Earls over Aeroquip.. although Aeroquip has some real nice quick disconnects.

[Grady Clay]

Ronin,

I have a dead head Holly on my 914-6 GT-2 race car. It works great for its intended purpose – racing. It feeds those Weber 46IDAs just fine for track use. The system I’m proposing is to address the issues of an everyday street 911 in hot weather. These are big deal issues and not easy to solve.

First is fire safety. Carbureted 911s need protection from accidental fires. I hate to think how many have been lost to fires that could have been prevented.

Next is drivability. The fun of a 911 is being able to put the power down when you want, not when the machinery feels like it. In hot or adverse conditions it takes some more engineering. Porsche engineers never anticipated carburetors in some of the extremes that we subject our cars to. It falls on us, collectively, to find the best solution for each circumstance.

I apologize for not mentioning Earl’s as a supplier. They have good stuff also.

Best,
Grady

[911pcars]

I found this out the hard way. Earls fittings are good. However, if an AN double banjo is on your shopping list, be aware the Earls version is not compatible with the Weber 40 IDAs. It's length does not provide the needed space for the hose connection to the single banjo.

Compare the length of the Earls double banjo fitting with those from Aeroquip and XRP.



Sherwood

[RoninLB]

Originally posted by Grady Clay

The system I’m proposing is to address the issues of an everyday street 911 in hot weather. These are big deal issues and not easy to solve.

First is fire safety. Carbureted 911s need protection from accidental fires. I hate to think how many have been lost to fires that could have been prevented.

"First is fire safety".
----- absolutely. A single small extinguisher is often inadequate. Fire safety should be part of the install design imo.

anyway. I found this Mallory #MAA 4307M bypass/BP regulator that will throttle down to low psi. There are not many options on this design that I could find. It lists for about $150, but a good shopper can find it for about $90. The "M" at the end designates marine, although in this instance it may only mean that they can add a 20% surcharge? The 8AN intake and bypass fittings have a rubber seal and a hose shop was necessary to locate an 8AN 90deg fitting. The rebuild kit is MAA 3178 and goes for about $25.
fwiw, the regulator internal restriction orifice may be an issue if shopping around.

3-Port Return Style, Gas/Alcohol
The Mallory Universal Competition Return-Style Fuel Pressure Regulator for carbureted engine applications. NOTE: This new regulator replaces both the MAL-4309 and MAL-4310 regulators.

New design utilizes dual layer diaphragm material that is not affected by today's gasoline additives. Hard anodized and works with gasoline and alcohol fuels. 100% billet housing allows for easy servicing. Easy to adjust High Flow Bypass System between 3 and 25 PSI. Includes vacuum boost/compensation port.
Multiple inlet and outlet ports for easy of installation.
Includes (2) #8 AN Fittings, (2) 3/8" NPT plugs, and Mounting Bracket.



ps: 8AN is almost 1/2" npt

[Grady Clay]

Ronin,

Cool. That looks like it might be the right part.
The -8 is about right for the return line and -6 for the supply.
What is it’s rated maximum flow rate?
What is it's low temperature spec?

OK, here is a diagram:
I need to edit it some more, put in the double banjos, test
port, and number the components.
I’ll also make the flow arrows bigger.

1) Fuel tank.
2) Electric fuel pump.
3) Filter.
4) Tee on supply side.
5) Banjo fitting at carb (4 total).
6) Tee on return side with pressure/sample port.
7) Fuel pressure sender (not yet shown).
8) Bypass pressure regulator.
9) Tee for pump relief (if used).

A karting friend from Albuquerque found the right set of pieces
for a fuel pressure/sample port. It uses a steel Schrader valve
and steel with Neoprene seal safety cap. Small, light weight
and a gauge or sample hose will just screw on or test the
pressure like a tire pressure gauge.
I’ll call him and post the links.


"
"
(C) Dr. Ing. h.c. F. Porsche A.G.


Best,
Grady

[}{arlequin]

That's awesome! Keep it coming and thank you.

So other than a fuel pressure gauge, the regulator that Ron posted is the only other "gadget" that needs to sit in the engine bay?

How do you set the pressure on it?

[Grady Clay]

Dave,

I would put all these components mounted to the front cross member (alu preferably) so they are below the fuel level in the tank and in a cool environment. As soon as you put more than insulated hoses in the engine compartment you are exacerbating the problem with heat soak in hot weather.

For track-only 911s it is a different story. There you open the deck lid between sessions, work at keeping everything cool, stand by with a huge fire extinguisher, and sometimes need rapid access to the components. Just the opposite is true for a street 911 (or even a street-track 911) because of the different issues.


It appears that the bypass pressure regulator that Ron found is adjusted with an Allen wrench and then the adjustment is maintained with the locknut. Those kinds of devices are usually not position sensitive so it could be easily adjusted from under the front of a 911.

This looks like a possibly good long-term solution; the regulator is from a major manufacturer and it has a rebuild kit. One of the more important issues here is serviceability. You have to be able to replace the fuel filter regularly. That should only require removing and refitting the four bolts for the front pan, a hose clamp for the filter, and two screw fittings. There should be enough hose to allow the filter to drop down slightly for good access with wrenches. You should be able to adjust the fuel pressure with only removing the pan. You should be able to service everything without removing the front suspension or fuel tank.

An issue is that many mechanics use clamps to pinch-off hoses when working on the fuel system. This is a Porsche approved technique with Factory hoses. The selection of hoses needs to take this into account.

This has equal applicability for all 356 and carbureted 914, 914-6 and more.

Come on all you engineers;
FIND FLAWS WITH ALL THIS.
What other questions need to be answered?

Best,
Grady

[Neilk]

Re: the mallory regulator.

Does it matter that the desired fuel pressure for a Weber carb is at the very low end of it's range? I am thinking along the lines of a torque wrench in that you don't want to use a 25-150lb torque wrench on a nut to be torquesd to 30lb. It's better to use a 10-50lb wrench, or so I have heard.

Can you connect a fuel hose with AN fittings to the regulator and hose clamps on the banjo fittings of the carbs?

What are some good quick release fittings that would work to connect the fuel pressure lines to the regulator (for engine drops).

Does anybody have a diagram of port on Mallory reg. so I could see how to route everything?

Thanks!