Black Ariel B&B Carburettor Data

[MGriffin]

I need some “trigger” info to get me near the mark on making up a needle jet and needle for the B&B carburettor on the model A. I’m considering starting with SU data for needle and jet correlation.

Anyone with a Black Ariel A or B running a B&B or maybe an AMAC that could offer some information?
Thanks.
Michael.

[nevhunter]

Can you show what the slide looks like. I think my B&Bs are earlier versions. Wouldn't AMAL needles be more varied and easier to get? Nev

[MGriffin]

Can you show what the slide looks like. I think my B&Bs are earlier versions. Wouldn't AMAL needles be more varied and easier to get? Nev

Hi Nev, AMAL needles are just too big.
The SU needle albeit with a “shanked” part is closer to the very worn and interfered with B&B needle I have.
Also….the B&B Needle Jet is very similar to to the AMAL type available today but overall smaller.

[cmfalco]

info to get me near the mark on making up a needle jet and needle

Luckily, all internal combustion engines need the same air/fuel mixture, and "all" 500 cc singles draw the same volume of air past the carburetor and into the cylinder on each intake stroke. As a result, "all" Amals use a 0.1065" ID needle jet, and 0.09865"–0.09870" OD needle. They could just as well have used a larger or smaller needle as long as they paired it with needle jets that resulted in the same annular area between them for the fuel to flow. So, pick the needle (or needle jet) you want to use, measure the diameter, and make the mating item accordingly to give the annular area calculated from the above Amal figures.

The above calculation tells you the dimensions for the straight portion of the needle at and somewhat above idle. Unfortunately, the taper matters at larger throttle settings, and needle tapers vary quite a bit. Needles for Mikuni VM series carburetors taper from the same 2.5 mm initial diameter to anywhere from 0.65 mm to 1.55 mm smaller at the end, so some trial and error will be involved. However, you should get pretty close by starting the taper at the same % throttle opening as it starts on an Amal, and tapering it from there at the same angle as an Amal.

Unfortunately, all of the above requires precision machining. A needle jet that is enlarged by only 0.0005" (e.g. from 0.1065" to 0.1070") flows 6% more fuel, and that's enough to affect the engine's operation. Reaming a 0.1065" hole to an absolute accuracy of no worse than 0.0001" is no mean feat. Of course, machining a 0.0987"-diameter steel rod, with the desired taper on the end, is no mean feat, either.

[MGriffin]

Thanks Charles….that all makes perfect sense and fine dimensional change and its effect is not lost on me or the science of combustion.

I’m still thinking to use an SU needle to fit the piston as I would rather modify the shank of a cheap needle than drill out the original piston.

Getting accuracy in making the jet will be a careful task but mixture can be accomodated by the multiple variations in the SU needle graduations available. I assume B&B may have supplied a few different needle jets like Amal does now but i have no idea.

SU needles look to be a good starting point and are graduated at 12 steps from 0.089” at the top. Amal needles are just too long.
SU needles are quite close in length.
M.

[cmfalco]

Getting accuracy in making the jet will be a careful task ...

The drawer of reamers holds the remnants of my failed attempts twenty or so years ago to make a needle jet (actually, not a jet, but a tool for jets).

Two size ranges are visible, for "ordinary" Amals and for the larger needle used in TT/GP Amals.

I failed, and my skilled technician failed, which doesn't mean someone else can't succeed. Or, if I tried again with twenty additional years of knowledge, that I might not succeed.

Showing that I haven't come to my senses and given up, shortly after I got my Sunnen hone a few years ago I bought .106 (range 0.106"–0.108") and .108 (range 0.108"–0.010") mandrels for it.

A significant problem we had with the reamed jets twenty years ago was rough IDs, which is something a hone is great for dealing with. Also, they can control diameters to 0.0001" allowing, a say, 0.106"-diameter hole to be enlarged to precisely 0.1065". I've had other things to keep me busy since getting those mandrels, but when I find time, I'm ready.

[Roger Gwynn]

Hi Michael, According to a parts book issued by Amal covering the carburettors of the amalgamated companies, B&B carbs had a choice of one needle and 2 needle jets, the latter were available as 'plain type' or 'needle type'. The description used was 'Std Jet nipple'. Actually looking again at the parts list I don't understand the terms and descriptions, also the pictures aren't clear and it is an amalgamation of information, so I am confused. If you don't have a copy of this I can copy it for you, it may help but there are no dimensions and only sizes for main jets are listed with conversion chart from B&B to Amal.

[MGriffin]

Thanks Roger…..is this the catalogue you are referring to?
If so, I could do with another copy please as mine ends at page 31 for some reason and has no B&B info in it.
Regards
Michael.

[Simon.Gardiner]

Anything useful in the B&B specs in the main website online library?
http://www.arielownersmcc.com/members_o ... /index.htm

(We don't seem to have a copy of anything Amal before 1937 so if anyone could provide an electronic copy of earlier catalogues....!! )

SG

[nevhunter]

Vintage AJS and Scotts ran Binks and they go well on both. I've never had much info on B&B but they go way back as a 2 lever carburetter with NO needle and they work well too if not monstered excessively. Lever operated throttles are optioned in vintage ARIELS.. Nev