Twin Carb fuel setup

[soulfire]

Hi guys,

some of you may or may not know that I am in the final stages of getting my twin-carbed 21/22r hybrid up and running.

I haven't realy dealt with carby fuel systems before, and I am just making sure that how I am going to run my fueling setup is going to be OK for my application. I do realise that I cannot have the fuel pressure anywhere over about 3 - 4 psi to fuel my Solex's

At the moment I have an intank fuel pump, which I want to feed a surge tank. From the surge tank, use an existing fuel line going into the engine bay, which will be plumbed into my electric fuel pump.

My question is, where do I need to position my fuel pump?
I was going to put it in the engine bay, on the strut tower, as it is a suck type pump.

In saying this, would it be beneficial to have the fuel pump as low as possible in the engine bay? Or am I going about this the wrong way, and should I keep my electric fuel pump in the boot alongside the surge tank?

I have a carby fuel pressure regulator that I will be using to keep the fuel pressure consistent to the carbs, would my filter come after the pump or the regulator?

Sorry for all the newb questions. I have done lots of research, and I've found lots of conflicting information (like people running twincarbs on mechanical fuel pumps :S)

I will be posting more information on my 22r build shortly, I am just trying to get everything ship-shape before my car hits the dyno for a run in tune

Cheers
Adam

[soulfire]

anyone?

or anyone know of any places or people i can see / talk to?
just want to get this fueling issue out of the way

[airfireman1]

Why do you want a surge tank? If you are only feeding about 3-4 psi your standard low pressure fuel pump will suffice. I have a electric low pressure fuel pump fitted on the chassis rail of my 28 feeding twin solex's with absolutely no problems. They will definately keep up with the carbs.
Cheers dave

[soulfire]

I was only thinking of having a surge setup as this cars primary use will be sprint days / drift days.

However, after thinking about it. The floats will still slosh around themselves causing all sorts of problems before I have fuel surging problems?

Thank you for your help tho. Atleast I know I can mount my electric pump in the engine bay with no worries.
Have you got your electric pump set on a relay to prime the carbs before you start?

Cheers
Adam

[airfireman1]

Hi, the pump is just hooked up to the ignition system and turns on with the ignition switched to on. To be totaly safe it would be good to have a relay setup so that it will only turn on with oil pressure. That is so if you have a crash the pump will turn off when the engine stops and you have a less of a risk of a fuel leak or fire. It is realy just a matter of having the pump run whilst cranking the engine then when the oil pressure is up the pump will continue to run. there is a thread on these forums somewhere with a wiring diagram to do this.
Cheers Dave

[mrshin]

Screw the oil pressure switch, use an LPG lock off switch, and one pump should be perfectly adequate for a carby setup.

[Rodger]

A surge tank is a very good idea for a track car even on carbs. It comes down to good flow rates and having fuel flow all the time and not so much a pressure thing.

I always had and have trouble when the tank was/is low, hilclimbing, sprints etc that need very little fuel in the tank. The OEM pick up is at one end and all the fuel would move away causing a drop to almost zero pressure (on my guage) on the longer right hand corners and the subsequent lean out of the engine at full noise.

Justen had a nice set up in the old 23, it was a simple gravity feed into a tank in part of the spare wheel well with the feed pipe fitted to the middle bottom of the main tank. Something I would do if I felt like modifying the tank in my 22.

As for fuel sloshing around in the bowls, admitedly there is some of that ,but compared to what happens when there is not enough fuel in there thus starving the engine, it becomes a non issue.

I'd be replacing the whole fuel line with -6 size or using both the line and the return line to give good capacity. As for placement of the primary pump, either end of the car is ok, comes down to access to the power circuits needed. Fuel filter before the pump though.

Agreed, the power needs to be done so it shuts off when the engine stops. Off the ignition circuit is indeed not ideal and I need to find that thread too Dave.

Regards

Rodger

[soulfire]

Thank you everyone for your input!

It's good to get some real-world experiences.
Are you suggesting to use both the fuel feed and return together on one pump? Say, tee them together and then feed the pump? Will this provide a better flow of fuel to the carburettors?

Where did you place your fuel pressure guage? Mine is an inline item, and I was going to place it just before the carburettors (assist with setting fuel pressure whilst tuning)

[Rodger]

Use the correct T with a larger fitting to suit -6 on the base and two fittings that match the OEM hose size across the top. At the surge tank use a -6 fitting and -6 hose to feed into the T located there.

Or if you can afford, run a length of -6 braided fuel hose the length of the car a chuck the old steel lines.

I put my fuel guage off the end of the SpeedFlow fittings at the left of my avatar. A guage adaptor fitting can be purchased that screws on to the -AN fitting. The guage mounted in the dash effectivley reads the line pressure and is a good indication of how well the pump can flow at full throttle, the most important time.

Regards

Rodger