38Dgas fuel return

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chips01
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38Dgas fuel return

Post by chips01 » Sat Jun 29, 2019 5:37 pm

Roger Pennington wrote:
Sat Jun 29, 2019 2:53 pm
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

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?
Now I am confused. I do not have the disc as in the image.
return.jpg
return.jpg (48.26 KiB) Viewed 757 times
My return pipe fitting is in the ally that does not have any hole or disc in it.



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38Dgas fuel return

Post by scimjim » Sat Jun 29, 2019 5:39 pm

AFAIK if you have the brass fitting, it’s drilled. The disc is behind the brass fitting.


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38Dgas fuel return

Post by gtcse8 » Sat Jun 29, 2019 5:41 pm

Close the float and blow through the bottom pipe, there should be air coming out of the top.

Very strange in deed as I have never come across this before.
And the brass pipe is Deffo a factory fitting as you can clearly see the distorted ring in the alloy at the base of the brass tubes.


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38Dgas fuel return

Post by Roger Pennington » Sat Jun 29, 2019 5:46 pm

The "disk" is the other end of the pipe, the end that's in the base of the hole in the ally. It's an integral part of the brass pipe stub, mine was removed because on an old carb the return pipe was loose and leaking, but it had been pinned previously, and the only way to get it out was by destroying it, so the end of the stub (in the photo) was the only bit left. By this time I'd discovered serious wear in things like the throttle quadrants, so I ended up replacing the carb.... So in effect the stub you are looking at in your photo, has a blind end, except for the tiny hole in the middle.


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38Dgas fuel return

Post by Roger Pennington » Sat Jun 29, 2019 6:07 pm

Here's another archive shot which perhaps makes the point - this is the pipe stub after the pin had been removed, but before the stub was pulled out of the carb. You can see the "blind end" of the stub. (the hole in the side is where the pin was inserted, of course)

Carb Pipe 02.jpg
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38Dgas fuel return

Post by chips01 » Sat Jun 29, 2019 6:25 pm

gtcse8 wrote:
Sat Jun 29, 2019 5:41 pm
Close the float and blow through the bottom pipe, there should be air coming out of the top.

Very strange in deed as I have never come across this before.
And the brass pipe is Deffo a factory fitting as you can clearly see the distorted ring in the alloy at the base of the brass tubes.
I cannot thanks you guys enough, amazing support. When float is closed there is no air coming from the return pipe. I have two choices. Leave it alone and continue without fuel return or attempt to drill a 1mm hole in the ally.



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38Dgas fuel return

Post by gtcse8 » Sat Jun 29, 2019 6:39 pm

Can you actually see into the return pipe, the hole may just be blocked with crud.
The hole MUST be in the BRASS pipe, not Ally.

The "disk" is the other end of the pipe, the end that's in the base of the hole in the ally. It's an integral part of the brass pipe stub ???

Not on the pipes I have pinned over the years, it was ALWAYS a separate, loose disc.

I don`t think Weber would have gone to the trouble of using a Flat nosed drill to produce the pipe before drilling such a precise hole in the centre.


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38Dgas fuel return

Post by Roger Pennington » Sat Jun 29, 2019 6:52 pm

All I can say is it certainly wasn't a separate disk on the one I dismantled, it was the end of the stub (as clearly shown in my second photo).


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38Dgas fuel return

Post by chips01 » Sat Jun 29, 2019 7:04 pm

gtcse8 wrote:
Sat Jun 29, 2019 6:39 pm
Can you actually see into the return pipe, the hole may just be blocked with crud.
The hole MUST be in the BRASS pipe, not Ally.

The "disk" is the other end of the pipe, the end that's in the base of the hole in the ally. It's an integral part of the brass pipe stub ???

Not on the pipes I have pinned over the years, it was ALWAYS a separate, loose disc.

I don`t think Weber would have gone to the trouble of using a Flat nosed drill to produce the pipe before drilling such a precise hole in the centre.
At the base of the brass fitting is a conical form that would be the same as left by a drill bit. There is no flat area and I have probed with a large needle and there is no evidence of any type of hole or anything blocking a hole.



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38Dgas fuel return

Post by Roger Pennington » Sat Jun 29, 2019 7:14 pm

Given the size of the hole, whatever amount of air is coming through by the "blow test" is likely to be small, and may be difficult to detect. If you have one (or can borrow one) a vacuum brake bleeder, (like a mityvac or similar device) might be a more accurate way to test it. I've just tried that on another carb, and it won't hold a vacuum, proving the existence of a hole.


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38Dgas fuel return

Post by gtcse8 » Sat Jun 29, 2019 7:51 pm

Roger it looks like a turned part in the picture with the £ coin


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38Dgas fuel return

Post by Roger Pennington » Sat Jun 29, 2019 8:24 pm

gtcse8 wrote:
Sat Jun 29, 2019 7:51 pm
Roger it looks like a turned part in the picture with the £ coin
Yes, it seemed to have just perceptible concentric ridges, which tend to suggest that. Also it's noteworthy that the "tube" part of the stub, where it's inside the alloy carb body, wasn't a constant cross-section, it had a narrower portion towards the top, which was then secured by the staked ring that can be seen round the pipes in both my last photo and Chips' previous photo. It made the pipes very difficult to extract! This is the remains of the input stub IIRC:

Pipe Stub.jpg
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38Dgas fuel return

Post by AJL Electronics » Sat Jun 29, 2019 8:34 pm

Roger Pennington wrote:
Sat Jun 29, 2019 6:52 pm
All I can say is it certainly wasn't a separate disk on the one I dismantled, it was the end of the stub (as clearly shown in my second photo).
I concur. The ones I have dismantled are one piece brass that look like blanks, but feature the very tiny 'jet' at the carburetter end. It is essential for the restriction to be there, else the fuel will flow down the easiest path which is the return. It acts as a pressure relief when the float valve is closed.


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38Dgas fuel return

Post by scimjim » Sat Jun 29, 2019 9:25 pm

chips01 wrote:
Sat Jun 29, 2019 6:25 pm
I cannot thanks you guys enough, amazing support. When float is closed there is no air coming from the return pipe. I have two choices. Leave it alone and continue without fuel return or attempt to drill a 1mm hole in the ally.
the third choice as suggested is to tee the return pipe into the feed line, with a restrictor inline.


Jim King

SECURE DRY STORAGE FOR YOUR SCIMITAR

Current: SE5 (8Ball), TI SS1 (snotty), 1600 SS1 (G97), 1600 SS1 (C686CCR), 2.5TD SE5a (diesel 5a), 6 x random other SS1s.
Previous: SE5, 3 x SE5a, 2 x SE6a, 3 x SE6b, GTC, 2.9i GTC, 3 x 1600 SS1, 1300 SS1, Mk1 Ti Sabre, Mk1.5 CVH Sabre
Chief mechanic for: 1400 K series SS1 (Megan3), 1400 CVH EFi SS1 (Grawpy), 1300 SS1 (Number One) & Sarah's coupe.
CURE THE FAULT - NOT THE SYMPTOMS

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