1927/8/9 Brown and Barlow 123-5 Carb help

[Daren W Australia]

Hi,

 I'm working on my 27/8 600cc sv and 29 600cc sv Douglas, Brown and Barlow 123-5 carbs.

 I have one complete (1) in 2nd photo is this the correct lid ?

 one that needs choke slide, needle, float and lid (2)

 one that needs almost everything but the body and bowl (3).

 Is there a supplier of parts for these online or do you have these bits in your garage ?

 Thanks Daren

[cardan]

Hi Daren,

Very difficult to answer your questions, because the 123-5 doesn't appear in the usual B&B literature, which would have us believe that the 123 carburettor wasn't fitted with a pilot jet, and yet the 123-5 clearly is. Perhaps it was made specially for Douglas?

Also 1928-1929 crosses the boundary between the old firms (AMAC,B&B, Binks) and the new (AMAL). Technically a B&B wasn't available in 1929, yet I bet they were supplied. Were some sold with AMAL float bowl lids? I don't know, but yours it the early AMAL type. I'd guess they had B&B lids originally, even if supplied in 1929.

Parts? I've suggested asking seller b561 on ebay before: he makes lovely parts and reconditions carbs, though more AMAC than B&B. Here's an example: https://www.ebay.co.uk/itm/143927411703

Here are the relevant parts lists, even though the 123-5 is not mentioned specifically.

Cheers

Leon

[cardan]

Looking further, I see from B&B List 26 (maybe 1927) that the 123-3 had a pilot jet.

Are we sure that the 123-5 is big enough for a 600?

Leon

[Daren W Australia]

Hi Leon thanks have found him now will contact tonight

I have this printed www.barnstormers.co.nz/147/brown-barlow-carburettors-bb/

and this www.barnstormers.co.nz/barnstormers/wp-content/uploads/2009/10/Carburettors.pdf

found this www.vintage-motorcycle-spares.co.uk/brown-and-barlow-29-c.asp

would love to contact this guy www.flickr.com/photos/145850402@N06/25546706277/ but not sure how ?

Thanks Daren

[cardan]

Before you go too much further, I think you'd better double-check the size.

It seems the 123-5 is the smallest of this pattern of B&B - only 0.71" bore. This might be fine on an 350cc EW, but it's very small for a 600? Some sort of 121 might be better - perhaps the 0.78" bore model?

Leon

[Daren W Australia]

Hi Found this in the spare parts list E/28 & F/29 600cc Daren





[add image. 29Mar21 -Doug]

[Doug]

Daren,

The 1928 F/G28 handbook shows the carburetor with fixed jet and a gauze at the base of the mixing body. The 1929F/G29 handbook touts the 'new' (for Douglas anyway) semi-automatic B&B with a needle. I think B&B had been offering both for several years. Both used the 123-5 body. Or they look identical, I do not know if they both have the same 123-5 number cast on the side.

I am not sure where the 123-5 nomenclature comes in. I assumed it was the equivalent of 123/5 in the B&B spares list, but then why they just did not specify it under the mixing body (no number given) I don't know. Note 123/5 is not assigned to anything else shown.

-Doug

[cardan]

The 1929F/G29 handbook touts the 'new' (for Douglas anyway) semi-automatic B&B with a needle. I think B&B had been offering both for several years.

Correct - in fact B&B introduced their "semi automatic" carb, with the size of the main jet aperture controlled by a tapered needle attached to the throttle slide, in late 1913 for the 1914 model year. What a clever and long-lived idea! What is surprising is that from 1914 until the end of B&B at the end of the 1920s there were always carbs offered without a needle. Cheaper to make, presumably.

The pilot jet (a path for idle mixture to bypass the usual path when the slides are fully closed) was also a B&B innovation. From 1916 models, when they were on the outside of the mixing chamber, but from 1924 the passageways were internal. Like the tapered needle, you could get B&B models without a pilot jet until the end.

The 123-5 is a late model B&B, presumably built by B&B specially for the 350 EW. It has both tapered needle and pilot jet, so it's a "top of the line" job. It's not in the usual B&B brochures, but there are carbs like the 123-3 with similar spec.

However the bore of the 123-5 is only very small (0.71"); I think too small for a 600. From the B&B tables, the appropriate carb for a 600 twin is probably a 121 model (0.78" bore), maybe a "121-5". Pity Douglas doesn't just list the model! The key features would be needle + pilot jet + 0.78" bore + mount to suit 600 Douglas manifold.

Cheers

Leon

[cardan]

The table above is for no-needle models; the 121-N (with a needle) has a larger jet (0.033")

Leon

[cardan]

I had a dig in the shed, and came up with two B&B bodies of the type under discussion.

On the left is a "121 type" carb, no pilot jet, 0.78" bore, no cast in ID.

On the right is a "123-5" carb, with pilot jet, 0.71" bore, 123-5 cast on the left side of the body.

Both use a 15/16" throttle valve (slide), and a 1" stub mount (although the 121 has the optional reduction sleeve to 7/8" stub).

Obviously "123" and "121" pilot jet bodies look similar from the outside. Perhaps the easiest way to tell them apart (other than the 0.71 or 0.78" bore) is that the 121 is taller at 3.23", compared with the 123 at 2.93".

Presumably the 123-5 is for a 350 EW, and the 121 with no pilot jet is the type in the 1928 E28 600cc parts list, but Daren's image shows a pilot jet.

From elsewhere, we know that 1930 600s used the unusual updraft AMAL 5/116/S https://www.douglasmotorcycles.net/index.php?topic=8679.0 This carb has an even bigger bore: 7/8"

Leon