Fuel system questions..., Does this look right? Options

[FourBlades]

Can y'all check my planned fuel system for my carbed 914?

Where do people recommend attaching a front mounted fuel pump?
Anyone have pictures of their setup?



Are two fuel filters overkill?

Any favorite fuel pressure guages or regulators?

Is there a better way to cap the small nipple than the old bolt n clamp method?

Thanks,

John

[McMark]

Looks good.

The stock front mounted pump system is a good way to go. Easy access without removing the tank.

Two fuel filters is not a bad idea.

A like plugging lines with the bit-o-hose and a bit-o-solid-steel-rod method. Just don't braze, weld, or otherwise permanently disable it. Options are never bad. (IMG:style_emoticons/default/wink.gif)

[type2man]

Looks good.

The stock front mounted pump system is a good way to go. Easy access without removing the tank.

Two fuel filters is not a bad idea.

A like plugging lines with the bit-o-hose and a bit-o-solid-steel-rod method. Just don't braze, weld, or otherwise permanently disable it. Options are never bad. (IMG:style_emoticons/default/wink.gif)

(IMG:style_emoticons/default/agree.gif)

My 914 is setup just the way yours is. The only thing I dont like is that my fuel pump(noisy Facet) is up by the steering rack and would be a mission to change out if need be. I plan to install a rotary one in engine compartment where it would be easy to swap out in case it takes a dump.

Patrick

[Cap'n Krusty]

Looks good.

The stock front mounted pump system is a good way to go. Easy access without removing the tank.

Two fuel filters is not a bad idea.

A like plugging lines with the bit-o-hose and a bit-o-solid-steel-rod method. Just don't braze, weld, or otherwise permanently disable it. Options are never bad. (IMG:style_emoticons/default/wink.gif)

(IMG:style_emoticons/default/agree.gif)

My 914 is setup just the way yours is. The only thing I dont like is that my fuel pump(noisy Facet) is up by the steering rack and would be a mission to change out if need be. I plan to install a rotary one in engine compartment where it would be easy to swap out in case it takes a dump.

Patrick

Bad plan. Fuel pumps should ALWAYS be mounted lower than the bottom of the fuel tank. The Cap'n

[McMark]

Sorry, Cap'N, I meant that since he's already planning on front trunk mount, he should mount it in the 75/76 stock location, directly under the tank. Easy to get to and still under the tank.

[jd74914]

Why not install a return line from your carbs? Its not much more expensive and you won't have to plug the other tank line. Plus, you'll always have cooler gas at your carbs.

[ahdoman]

Here's a pic of my fuel line setup. This is for a 2.7 CIS but the concept is the same. If you are going carbs I highly recommend the CB rotary pump. For carbs you need high volume with low pressure. The CB rotary is what does that. Also, if you use the CB there's no need for a pressure regulator but a return line is a good idea.

[SirAndy]

If you get the CB rotary pump you don't need a fuel pressure regulator.

And a return line would be a good idea as well ...
(IMG:style_emoticons/default/shades.gif) Andy

[FourBlades]

Ok, thanks for all the suggestions.

I have a Carter rotary I got from Jake. It turns out it has a built in regulator
set to 3.5 psi. I will still add a pressure guage to be sure I am getting
enough at the carbs.

The stock 75/76 location sounds good, anyone have a picture of where that
is? I was planning on front mount, not necessarily front trunk.

Where do I plumb in the take off for a return line? Seems like it would reduce
the pressure at the carbs. I do have all 4 CFR lines so I could do it.

John

[ahdoman]

The Carter rotary is also a great pump. It's just a little noisier than the CB Rotary.

If you put in a return line I really wouldn't use a pressure regulator. It will only put the system out of balance. If you think about the "balance" of the system; Your carbs will need varying amounts of fuel depending upon how hard you are driving. A pressure regulator is a bandage. The return line allows a relief point for the extra pressure. If your car is at idle the extra fuel returns back to the tank.

If you incorporate a return line the system is usually a "loop". The idea is to keep the entire system "pressurized to the 3.5 psi. You'll need to put dual nipple banjo fitting on each carb. The send line hits the first carb, the output goes to the second carb input, that carb output goes back to the return line.

[FourBlades]

Thanks Steve. I will look into the return line.

I think I may end up putting the pump in the front trunk. Makes it easy
to service the pump and change the filter. I plan to put some rubber mounts
on it to quiet it a little.

John

[bperry]

The Carter rotary is also a great pump. It's just a little noisier than the CB Rotary.

If you put in a return line I really wouldn't use a pressure regulator. It will only put the system out of balance. If you think about the "balance" of the system; Your carbs will need varying amounts of fuel depending upon how hard you are driving. A pressure regulator is a bandage. The return line allows a relief point for the extra pressure. If your car is at idle the extra fuel returns back to the tank.

If you incorporate a return line the system is usually a "loop". The idea is to keep the entire system "pressurized to the 3.5 psi. You'll need to put dual nipple banjo fitting on each carb. The send line hits the first carb, the output goes to the second carb input, that carb output goes back to the return line.

The CB pump I have is made by carter.
CB/Carter pump

But my real question is with this "loop" return configuration.
Have you actually set this up and measured the fuel pressure being supplied
to the carbs in this configuration?

The reason that I ask is I would be concerned that without some form of
back pressure to limit/restrict the flow *after* the carbs
that there will not be consistent or sufficient pressure
maintained to the carbs to ensure proper flow into them.

Normally, what I've seen for return systems, is a back pressure regulator
with the excess pressure being returned. This type of regulator doesn't
limit flow like the simple regulators the go between the pump and carbs.

The setup you describe above has no form of back pressure other than
the smaller size of the return line and the weight of the fuel pressing down
on the returned fuel.
I'm just curious if that is enough to work even when the gas tank
is near empty.


I would think in the absences of any sort of back pressure regulator,
to keep pressure/flow consistent between the carbs,
perhaps it would be better to create a double loop with a "loop" around
the carbs that is feed and returned as part of the bigger loop
rather than a simple loop with the fuel entering and exiting each
carb in series.


See figure.



I like the simplicity.
I have no idea which if either would really work.
So my real question is still, have you ever hooked up a return
line like this and measured pressure at the carbs or actually run
a car this way to see that this method works including when the fuel
tank is near empty?



--- bill

[FourBlades]

Bill,

Those are some good questions. I can see how the pressure
at the carb inlets could drop if the return line presents a lower
resistance path for the fuel. Maybe a restrictor after the carbs
would provide enough back pressure? Like maybe a constriction
down to 2 mm.

Quite a few people, including major racers, told me that they
never ran a return line and never had any trouble. Living in
FL where it gets kinda warm I can see the potential for fuel
boiling though.

I definitely want a fuel pressure gauge before the carbs to
see what is going on. There is a VDO one from Jegs for
only $20, 0-15 psi.

John