Do twin SU's need a fuel return

[RB30X]

My question is do our twin SU's really need the fuel return line?

 

From what I can tell from researching, the existing 6mm return line has a reducer in it at the tank anyway, so it isn't really 'returning' the fuel to the tank to release pressure, just keeps it recycling to reduce vapour lock.

 

The reason I ask is I've sold the triples and resinstalling the SU's. The triples never needed a return and they run on the same pressure so 'why' would the SU's need it.

 

Cheers

[pauly_adams]

truely they dont i have run them without a return with no problem although now i do have a return line

 

cheers pauly

[Zedman240®]

I think with the return there is no way the fuel pump can "force" the fuel into the bowl. Say if you still had the mechanical pump, and revving on the freeway at 3000 rpm for hours, any excess fuel will return to the tank. I'd run one..and the restrictor is on the  original metal fuel rail where the return hose connects at the front of the motor.

[RB30X]

I've since done some testing with a pressure gauge and with the return hooked up it recorded no pressure (at rpms less than about 3K) with the mech pump and electric going. Then if i crimped off the return pressure went straight up to 3 psi and stayed there??? Aren't electric fuel pumps designed to mantain a pressure anyway, you hear em go until they've filled the lines and then they stop or slow down.

[pauly_adams]

theres normally a cap on the end of the return with a small hole in it which keeps pressure up. it will work fine without though, this comes from personal experience, from what i can gather they used the return line in case there is to much pressure stored in the carbie IE when your hard shifting the engine its revving hard then when you clutch there is no need for such a volume of fuel which could cause a build up of pressure in the lines and carbs.

 

hope this helps.

 

cheers Pauly