fuel return tube

[Doehring]

My '72Z's fuel return pipe is closed. So I tried to open it with a wire. That thin wire broke inside the tube and now I'm at the end of my wisdom.

Question 1: What will happen to my driving with a closed fuel return pipe, are there any dangers like SU carb overflow and fuel dropping out and on the hot exhaust or too rich mixture or ... ?

Question 2: Any ideas what to do? The possibility to get a tube at a wreckyard is near to 0 here.

Question 3: Is it an easy job to take off that tube from the rear (tank) and to work from that end and is there anything to take care of, like valves for instance ?

Thanks in advance

Rolf

[240ZX]

If you have the stock fuel system, you definitely need to have an operational return line. Fuel pressure is regulated by that little rectangular block at the rear of the fuel lines that run next to the cam cover. It has a small metering hole that provides the correct resistance to maintain approximately 4 psi to your SU's. The fuel that passes through the metered hole returns to the tank through the return line. If the return line is blocked, you will have too high a pressure at your SU's, resulting in probable float bowl overflow, because the needles and seat are not designed to handle much more than about 6 psi. The newer the needle and seats, the more pressure they will hold. Anyway, you need to get that return line unplugged or replaced. It should not be a very difficult exercise. Hope this helps you out a little....good luck!

[Doehring]

240 ZX, thank you for the good explanation, esp. concerning that little block. I always wondered how it works.

Over the weekend I took the fuel return pipe off at it's end and pushed the wire out from the rear.

Rolf

[beandip]

That is good to hear ! I was going to worn you not to use copper line in its place. I know some have and it is dangerous if it isnt the proper stuff. I can imagine that used fuel lines would be hard to fine over there . Did you get the blockage out of your line after you removed the wire ?

[Doehring]

Beandip, yes, I got the blockage out. Before I pushed with the long core wire of a bycyle's rear brake-drawing into the fuel line I blew W40 into it overnight. The blockage was a little piece of rubber (maybe from the upper rubberhose connection between the body's return line and the return line around the engine's cover). That was pressed by the first wire, the one that I used from the front and that broke, inside the fuel line at one of the bends at the firewall.

By the way, you mentioned copper. What copper would be the right one in case someone of us has a similar problem and goees for copper?

Thanks

Rolf

[240ZX]

The reason one would not want to use copper lines for fuel lines is safety!!! Copper lines are pretty much in an annealed state (soft) and when subjected to movement and vibration, over a period of time, they will work harden (get brittle) and fail. A failure is likely to happen on or near where the line becomes flared, for a fastener. So do yourself a favor and use an appropriate steel fuel line.

[Doehring]

Thanks 240ZX. Some time ago I saw a realy very old french motorbike that had a nicely polished copper fuel line. Cyclists always lived in danger.

[beandip]

I have been told that some of the Jags. had used copper fuel lines , I have no experience with british cars but this is what I have read. since you are in europe I just thought that this might have been an option to you, but dident want you to try common copper tubing. As was stated above this line is soft and will easily crack with vibration. The lines that Jaguars use must be of a different alloy or not really copper at all , in any case use steel. I have read some real wonders on this web site , every thing from using brake fluid in the SUs insted of oil , to removing the fuseable link in the main power line to the starter. :classic: