Petrol return feed from Carb

[The Surveyor]

There is a return outlet from the carb (standard 38 DGMS Weber) on my 1976 3000M which was sealed with a short rubber hose with a bolt in the end. I've seen a couple of cars with a return feed back to the petrol tank, and some without.

You'll see the current arrangement above the supply pipe below:-



Does the carb need the return flow to avoid any pressure build-up when the float chamber is full, or is the 'bolt in the hose' the normal way of plugging this spare outlet. Is there a neater way of plugging the outlet if it's surplus to requirements..

Thanks for any input guys.

Paul

[tegwin]

The return on the carb is there incase the needle valve gets jammed open and the float chamber fills with fuel and keeps on filling.... the excess fuel will eject through the overflow...

On my car they were not connected to anything.... which allowed the fuel to drip onto the zorsts if the carbs overflowed...

I fitted small pipes and it drains out down under the wing onto the floor... not that I have any overflow issues...

[Adrian@]

Paul, In the case of the 38 DGAS the return is there as an overflow, but IF you look into the pipe you will see that this is not a normal outlet and is a restricted outlet which causes back pressure within the fuel pump. IMHO you need to take and return it to the tank, If there is too much pressure there is a possibility that the inlet will blow off and spill petrol over the engine.
Adrian@
Edited to say fuel pump

Edited by Adrian@ on Thursday 9th April 12:09

[youngnick1]

Following on from Adrian's comment, it may be worth reading this topic:

http://www.pistonheads.com/gassing/topic.asp?h=0&a...

Alan

Edited by youngnick1 on Wednesday 8th April 07:33

[Slow M]

It would be nice if fuel return lines would be fed back to the fuel tank.
I would have thought that it would be difficult to remain oblivious to the state of the planet.

[Seabass]

The original reason for having a return line to the tank has nothing to do with excess or over pressure situations. Fuel into the float chamber is still regulated by the float needle valve. The float chamber is not pressurised - this would effect the fuel flow through the jets.

The return was designed to alleviate fuel vaporisation in the fuel inlet lines and therefore starvation in hot climates. The return feed would ensure a constant cool flow of fuel in the system where some fuel was returned to the tank.

Many people do block the return line and although aesthetically undesirable the main consideration should be to under bonnet temperatures and the likelyhood for vaporisation to occur in a given installation. As mentioned anyone working on the fuel system should check the integrity of fuel connections including the inlet and outlet barbs on the carb.

Slow M said:

It would be nice if fuel return lines would be fed back to the fuel tank.
I would have thought that it would be difficult to remain oblivious to the state of the planet.

Lol. Not too certain what your hinting at there? I'm sure none of us vent unused neat fuel onto the road!!

JC

Edited by Seabass on Thursday 9th April 11:44

[Slow M]

Seabass said:

Slow M said:

It would be nice if fuel return lines would be fed back to the fuel tank.
I would have thought that it would be difficult to remain oblivious to the state of the planet.

Lol. Not too certain what your hinting at there? I'm sure none of us vent unused neat fuel onto the road!!

Seabass, the whole hinting thing involves subtlety, something I've never quite mastered.

tegwin said:

...I fitted small pipes and it drains out down under the wing onto the floor...

[Seabass]

Indeed! Perhaps I should have read Tegwins post... Doh