1600 8 valve fuel pump for su carb

[hamishh]

so I finally found myself a HIF44 su for a good price and am gonna put it on my 1600 8 valve. quick question about the fuel pump though. this one has the one inlet and the two outlets and as far as I am aware on is for the throttle pump and the other is the main feed for the carb. which one is the one for throttle pump and can it be brazed up without causing too much drama for anything else. Thanks

[ScottieJ]

Small outlet is the fuel return back to the tank

[hamishh]

I think you may be thinking of different fuel pump. The one i have attachrd is the one i got. Both have fuel coming out of them

[Darrell]

Is Scottie not correct

[hamishh]

Well i dont know i ask cos bith these ones pump out fuel and there is a seperate line not part of fuel pump which returns from carb. This is the pump like the one on my 1300 which only has the fuel coming out of the one port. This is why i ask not being rude or nothing

[ScottieJ]

It's a fuel return to the tank, well that's how I've always had it set up in mine.

There's no fuel return from an SU carb.

[Anton]

Yeah, I always thought that it was a fuel return line, but since I have had an electrical pump in mine, I never really bothered to find out for sure - I just remember people talking about the fuel return lines on the mechanical pump.

[hamishh]

Thanks i thiught it was a return but was not sure cos it had fuel coming out of it too so i guess pump is rooted.

[Anton]

It's supposed to do that if it needs to regulate fuel pressure. That's why it's plumbed back to the petrol tank.

[twiss]

Yes, the stock pump regulates the pressure for the carb. The SU uses similar fuel pressure to the stock carb, so will work fine.
The facet type electric fuel pump will naturally limit its pressure. When pressure builds up inside the pump, the diaphragm will do less work and create less pressure.

The stock pump needs better regulation as the pressure will build up quite a lot at high revs. If you ran the mechanical pump with no carb attached, all the fuel should flow out of the outlet to the carb.
If you block it off with your finger, then pressure would build quickly all the "excess" fuel would flow back through the return-to-tank outlet.