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38Dgas fuel return

Posted: Sat Jun 29, 2019 10:58 am
by chips01
Curious one. My car has fuel return piping from 38Dgas back to fuel tank but the return fitting on the carb has not been machined through and thus return is blanked off. Is this normal and do I have to drill out the return fitting to allow fuel to return to tank?

Many thanks for your help.

38Dgas fuel return

Posted: Sat Jun 29, 2019 11:39 am
by peter freeman
The Coupe's and 5's do not have a return line - I cannot think it is so important

38Dgas fuel return

Posted: Sat Jun 29, 2019 11:44 am
by chips01
peter freeman wrote:
Sat Jun 29, 2019 11:39 am
The Coupe's and 5's do not have a return line - I cannot think it is so important
Just seems strange to got to all the cost and effort of providing return fuel line to the tank and not using it.

38Dgas fuel return

Posted: Sat Jun 29, 2019 12:04 pm
by Roger Pennington
peter freeman wrote:
Sat Jun 29, 2019 11:39 am
The Coupe's and 5's do not have a return line - I cannot think it is so important
Peter, the first half of your statement is correct, but the conclusion may be the wrong way round - perhaps it was important (especially in hot conditions) and that's why it was introduced in later (approximately Se6a-onwards) versions? :)

As far as Chips' question is concerned, if your car has all the return pipework present and correct, but no fitting on the carb, then I'd guess it's quite likely that a PO has fitted an old carb (without the return) for some reason? Which model variant of carb is it (it should be stamped into the carb base)?

38Dgas fuel return

Posted: Sat Jun 29, 2019 12:13 pm
by Terry H
Also, what year and model or series car is it fitted too. My 1976 SE6 did not have a fuel return fitted.
Regards Terry H

38Dgas fuel return

Posted: Sat Jun 29, 2019 12:31 pm
by chips01
Roger Pennington wrote:
Sat Jun 29, 2019 12:04 pm
peter freeman wrote:
Sat Jun 29, 2019 11:39 am
The Coupe's and 5's do not have a return line - I cannot think it is so important
Peter, the first half of your statement is correct, but the conclusion may be the wrong way round - perhaps it was important (especially in hot conditions) and that's why it was introduced in later (approximately Se6a-onwards) versions? :)

As far as Chips' question is concerned, if your car has all the return pipework present and correct, but no fitting on the carb, then I'd guess it's quite likely that a PO has fitted an old carb (without the return) for some reason? Which model variant of carb is it (it should be stamped into the carb base)?
Many thanks. The code stamped on base is 020472.

38Dgas fuel return

Posted: Sat Jun 29, 2019 12:33 pm
by chips01
Terry H wrote:
Sat Jun 29, 2019 12:13 pm
Also, what year and model or series car is it fitted too. My 1976 SE6 did not have a fuel return fitted.
Regards Terry H
The car is 1 1977 SE6a

38Dgas fuel return

Posted: Sat Jun 29, 2019 12:47 pm
by Roger Pennington
Yes, I saw from some of your previous posts that you had asked about Se6as :wink: Fuel returns were introduced at *roughly* the point of the Se6/6a changeover.

There should be another number on the opposite side of the carb base (the autochoke side IIRC) - it should specify the carb type, eg 38DGAS 3C or whatever.

38Dgas fuel return

Posted: Sat Jun 29, 2019 1:16 pm
by chips01
Roger Pennington wrote:
Sat Jun 29, 2019 12:47 pm
Yes, I saw from some of your previous posts that you had asked about Se6as :wink: Fuel returns were introduced at *roughly* the point of the Se6/6a changeover.

There should be another number on the opposite side of the carb base (the autochoke side IIRC) - it should specify the carb type, eg 38DGAS 3C or whatever.
Many thanks for your help. 38DGAS 3C and it has two fuel line fittings. One fuel in and one fuel return.

38Dgas fuel return

Posted: Sat Jun 29, 2019 1:31 pm
by scimjim
Are you sure it’s not drilled through? If it has a brass fitting it should be (although it’s a very small restrictor hole). If it’s not drilled, it should just be the alloy boss.

38Dgas fuel return

Posted: Sat Jun 29, 2019 2:05 pm
by chips01
scimjim wrote:
Sat Jun 29, 2019 1:31 pm
Are you sure it’s not drilled through? If it has a brass fitting it should be (although it’s a very small restrictor hole). If it’s not drilled, it should just be the alloy boss.
I have tried 1mm probe and the centre is closed. I was about to install an electric fuel pump and I was going to rely on the return pipe to cater for any over supply of fuel. What size of hole do you think I should machine? Many thanks, Keith

38Dgas fuel return

Posted: Sat Jun 29, 2019 2:17 pm
by scimjim
It’s about 1mm IIRC - if you really feel the need for a return line, you can just T one in?

38Dgas fuel return

Posted: Sat Jun 29, 2019 2:53 pm
by Roger Pennington
As Jim says, it's a very tiny hole (may even be smaller than 1mm) - it would be quite a lucky shot if you managed to get a pin thin enough, into the hole at the opposite end of the brass fitting. I presume it's designed that way to allow the delivery pressure to be maintained, while allowing excess to return to the tank. Here's an old picture from my archive of one that I removed, some years ago:

Carb Pipe.jpg
Carb Pipe.jpg (135.61 KiB) Viewed 641 times
Re-reading your original post, it's not quite clear what your current status is - you've got the original return pipes present, and a DGAS 3c carb which has a return stub; has someone disconnected the one from the other in the past, and blocked them off, or were the pipes correctly connected, and you're just inferring that the return is blocked, because you can't poke something through it?

38Dgas fuel return

Posted: Sat Jun 29, 2019 4:14 pm
by Laters
My original carb had a return where the carb I have now doesn't.
I'm not in the position to modify my current carb & as the return line is already fitted to the car may as well use it.
You can buy a t piece that has the return line restrictor already fitted.
That's what I am going to use on my car when I get around to sorting the fuel system out.

38Dgas fuel return

Posted: Sat Jun 29, 2019 4:18 pm
by peter freeman
Same engine and more or less same fuel tank as the earlier cars so I think the return line was fitted to stop the difficulty in starting when the early cars had been stood for a while and the petrol had drained back to the tank. Having a return line makes it easier to fill the carb.