The V8 Owners Forum -

Hello all,
Apologies if this has been done before but after scouring the internet for some time, I could not find a satisfactory answer.
I have a London Taxi as a project car. I’m putting in a 3.9 v8 with SU HIF44 carbs. The taxi was fitted with fuel supply and return lines.
Basically, what I want to know is, what should the ID of these pipes be? I will use a Facet Posiflow pump (3.5 to 5 psi) with non return valve and a prefilter. I’m guessing 8mm would be good for the supply but what about the return? Should it have a restrictor in it? Would I also need a regulator?
Sorry if this seems a bit simple but I’ve no experience with this sort of thing.
Many thanks.

I am sure that SU's don't have a fuel return. Once the float bowl is full, the needle shuts off the supply, and the pump stops delivering because it can't overcome the needle valve.

They have an overflow in case the needle valve fails in some way.

As for pipe ID, I would just match whatever the carb inlet is.

Chris.

P.S. Got any pictures?

ChrisJC wrote: ↑

Sun Jun 07, 2020 1:28 pm

I am sure that SU's don't have a fuel return.

Rover P6B does.

harvey wrote: ↑

Sun Jun 07, 2020 1:51 pm

ChrisJC wrote: ↑

Sun Jun 07, 2020 1:28 pm

I am sure that SU's don't have a fuel return.

Rover P6B does.

Yup - but a mechanical pump. The traditional SU pump would just stop when the carbs are full.

The SD1 has an electric pump in the tank. No return with that. The injection version an external high pressure pump with a return.

I was right with the part I quoted and answered, but you're right about the SD1, and the clue, "HIF44", was in the original post.

harvey wrote: ↑

Sun Jun 07, 2020 3:05 pm

I was right with the part I quoted and answered, but you're right about the SD1, and the clue, "HIF44", was in the original post.

I doubt it matters what version of the SU carb.

The P6B was dreadfully prone to fuel evaporation problems. I'd guess the fuel return system was an attempt to reduce that, with the simple and cheap mechanical pump.

Many thanks. So I think I’ll just use a single 8mm pipe and route it away from the exhaust and see how it goes. The baby 1.5 to 4 psi facet pump may be suitable in this case. I’ll put up some pics when it’s finished...

I've always wanted a sleeper black cab with a V8 transplant! Welcome along, look forward to seeing your ride when you get it all sorted out Eric!