914 Weber carb setup

[Fat Albert]

I have read the extensive comment regarding Weber carbs and viewed the Brant diagram which is very helpful.
My question is as follows:- I have used the Pelican fuel pump rated for maximum 5 psi and relocated same under the fuel tank with a single braided line to a filter then in line to the dual Weber carbs.
The return fitting at the bottom of the tank has been capped off.
The carbs are 48IDA and the motor is a big bore 2500cc stroked unit.
Is it necessary to use a regulator in the system if the pump is already designed to run such a low psi rating?
In other words my setup is the Brant diagram Option A without the regulator.
If a regulator is used should it be set up in a central position with equal length line feed to the dual webers?
I am unsure of the purpose of the return line as shown in Option B- if the fuel is regulated before reaching the carbs would not this fuel be consumed rather than be pumped back to the tank- and secondly the return functions from the second carb only rather than from both?
I apologise if these questions appear dumb as I have little understanding of required fuel flow for dual carb setups and any help explaining this would be much appreciated.
Regards,

Fat Albert

[Dave at Pelican Parts]

It can evidently be handy to be able to set a specific fuel pressure; I am told that some carbs "like" a little less and some a little more. If you run into one of those cases, a regulator is very good to have.

There are a couple of different ways to regulate fuel. One only allows a certain pressure past it. Those are what you use in a return-less system. The other actually plugs the "far end" of the fuel system, raising the pressure of everything between the pump and the regulator. The fuel does keep pumping, and excess fuel over the amount required to maintain the pressure is dumped into the return line, going back to the tank.

Which setup is better? I have no idea. I'm not a carb person. The FI pump works the second way, so that is what I'm familiar with.

--DD

[Fat Albert]

Dave,
Thanks very much for your input - it has helped greatly my understanding.
As I also have little understanding of carbs I have decided to get a Weber expert to look at my setup and make sure we have the best option- I will show him the Brant options also.
Once i get my act together I will send you some pics of my car.
Regards,
Fat Albert.

[jhora]

Albert...
PMO has a very nice fuel regulator for carbs...
works very well has the pressure gauge on it and has the return outlet which bleeds off the excess presure..
see here in a set of carbs I sold...

http://forums.pelicanparts.com/porsche-911-used-parts-sale-wanted/662414-fs-pmo-40-carb-kit.html

the lines don't need to be exactly even just a good even flow of fuel via a good pump and pressure regulator....the needle valve and float do the job of filling the fuel bowl

John

[John Rogers]

Here are some items when I raced a 2.8L type 4 stroker motor with Weber 48's. We ran 3.5 to 4 PSI fuel pressure, raising or lowering to change the enrichment. We found that 5 PSI was too high in most cases. We never ran a bleed off line or recirc line as the Webers did not need one and most of the vintage racers in the HSR Porsche 2L series never used them either. We used a Holly regulator and had the fuel pressure gauge in a line that connected the carbs after the fuel inlets. We found that to insure no starvation, we went with 150% of what the engine requirements were for fuel CAPACITY, not pressure. There are many racing sites that let you input parameters such as displacement, estimated HP, RPMs and other stuff and will tell you the GPH requirements. You can also check with a shop that runs engines like yours. One thing to note, a 2.8L four cylinder engine that puts out 180 to 200 HP at the rear wheels does not need as much fuel as the same size six making the same HP. A couple of final notes, I would suggest an air fuel meter and O2 sensor to keep an eye on that expensive motor you have as it takes very little time to melt a piston if one of the carb barrels gets starved! Last of all I would suggest a trip to the dyno to set everything up as Wayne Baker likes to say, 1 hour on the dyno is worth 4 or so at the track!

[Fat Albert]

To jhora & john rogers,
Thanks guys for your effort and advice which I have taken on board.
JR I will definitely go with the Holley regulator and include the air fuel meter and O2sensor.
We are currently getting 125HP on the dyno and with a little tweaking anticpate around 135 to 139 which would be pretty good for a 2500cc.
I am located in Brisbane Australia and compete in hill climbs & motorkhana events- my car is a 1974 914 ex California import. These are rare down here so any help I can get on these fantastic cars is much appreciated. There is no doubt in my mind that you guys are the world experts in the development of these cars and have strong ethics in their preservation and use .
Regards,
Fat Albert.

[Dave at Pelican Parts]

The inexpensive narrow-band O2 meters are just about useless, IMHO. Find yourself a wide-band O2 meter if you're going to use it for anything other than dashboard decoration.

--DD

[Fat Albert]

Thought I would convey response to fitting a Holley regulator and gauge as suggested.
The idle issues and stalling at low revs has been cured set at 3.5 psi.
The motor sounds great and cackles like a large Harley.
Last hill climb bettered PBT by 4 seconds with plenty left to go.

Thanks again all for your imput.
Regards,
Fat Albert.