Working out the plumbing details for my six conversion for the fuel lines. I've read a few threads and I'm still confused.

I'd like to keep the fuel pump in the front underneath the tank. (The 1975 car I'm staring with had it there to begin with.)

What sort of pump should I use to get the 3.5 to 4.5 lbs pressure I need for the Weber 46s? Hardi, Bosch, Rotary, Holley?

Do I need a return flow line?

If I have a pump that flows at 3.5 lbs, do I need a pressure regulator.

I also plan on installing a filter before the pump and one before each carb.

Thanks,

Karl

Carb fuel pumps are pretty idiot proof. The Purolator/Facet/Holley are all good. "I" have used a regulator in line for peace of mind.....

A fuel return line is not required for carbs.

correct, but search around a bit. I seem to recall that some people choose to use a return line for reasons beyond my understanding.

Cooling....in high heat areas, it's a must. Especially with the new fuels that flash off easier.

Wasn't there a Bosch pump used for some of the early carbed motors that had a return line inlet built into the fuel pump?

Okay, I understand the stock 914 FI fuel routing, venting, and return system pretty well.

For carbs, is this how it is set up...?

Fuel tank outlet -> Fuel filter -> fuel pump -> fuel line in center tunnel -> fuel pressure regulator -> fuel pressure splitter (or does the regulator split? -> individual fuel filters -> each carb's fuel fitting -> Stop!

Or do you want your fuel regulator before the tunnel? It would make sense to have the pressure regulator after the tunnel, as you will experience a pressure drop through the tunnel.

Are there any decent rotary pumps out there, our should I stick with a Holley?

BTW, all this is for a 3.2L six with 46mm Webers.

Thanks,

Karl

Yup. The factory pump for the 914/6 looks just like the FI pump, but doesn't put out anywhere near the pressure the FI units do. And they do have a return line through the tunnel just like the later FI cars. I wouldn't go looking for one though. Just use a replacement.

FWIW, I had a Facet on my first carb'd 914/4. The only tine you hear it is when the ignition is turned on and when the car is idleing quietly (which wasn't very often on that particular car). I kind of liked hearing it, that way I had a pretty good idea it was working. If I were looking for a pump for a carb'd car though, I would probably get a rotary pump.

Ginter's .02 for today. Must go mow the lawn and strip some more crap off the car now.

On a somewhat related, question. Are both of the fuel fittings on the tank bottom essentially the same?

Or is one specifically an inlet, and the other an outlet?

Thanks,

Karl

I think they are different diameter but more importantly, one (outlet) has a filter screen attached inside the tank. Probably good idea to remove the fitting and clean the screen after 30 years.

Here is a recent thread that might answer some of your questions.

Weber plumbing question

Yeah... that thread.. it went back and forth... I got pretty confused.

http://www.cbperformance.com/catalog.asp?ProductID=577

This the rotary pump from CB Perforamnce. If I mounted it up front, underneath the tank using the stock (1975) mount location, it sounds like I would be in good shape! Or will this not pump enough fuel for my big six?

Or... does someone else want to interjectect some more confusing information into this idiot's head?

Thanks,

Parts America stocks the Purolater 12S. Runs from 3.5-5 psi. They also have a nice filter (same manufacturer) that is clear, with replaceable inserts. Very nice to see whats in your filter - you can't see well in the translucent VW filters.

-Rusty

I am not sure why they include that filter w/ the CB pump. I threw it away. Running the Bosch original equip. type filter.

It doesn't matter how big the six is. If you're running carbs you need 3.5 psi.

Not as simple as that Mikey.....volume is also involved. If you have REALLY thirsty carbs, you might draw more gas than the pump can deliver.

What's to say that a 6 psi rated pump gets regulated down to 3.5 but due to volume the delivery to the carbs is like 2.0......

Yeap, he’s right. When we went to carbs on the 3.0 we tried to use that rotary pump. It can’t keep up with 40’s let alone 46’s. :toilet: I have a fuel pressure gauge in the cockpit and you could watch it drop when you run on the track. I went back to the Holley with an adjustable fuel pressure regulator you can get the combination from Summit Racing for about $115. Part HLY –412-802-1 it pushs110 gph. Get a fuel pressure gauge. At idle the pressure is at 7-9.

Just FYI on the pumps.

A stock 9146 carb pump has been watched on a hot rod 3.2 engine during a few dyno pulls and it keeps up just fine. My not work at the track... but it worked great for back to back to back pulls.


B