B33 carburettor settings

[Christouring]

Happy New year!

My '53  BSA B33 should have a 376 monoblock.
1.1/16" bore. 260 main jet. Throttle slide 3.5 & with meddle position 3 (bottom groove = richest)

It has though a 928 mk1 concentric.
Rather than go through all the permutations, can someone who has this type of setup let me know which combination works best.

Currently
This is a 28mm size so is between 1.1/16 & 1.1/18 bore.
I used to have it on 180 main jet, throttle 3 and all positions of needle with varying slight effects. I was told by Amal that it should be a 3.5 throttle & 260 main jet. Need position 2 or 3.
This is the current set up but it feels limited to 60mph though on a straight can hang on to 70mph so I don't think it is valve springs.

Currently without an air filter but have swapped between one & not without any noticible difference over the years.

[Christouring]

An update for those interested .
Standard/original book set up is
Monobloc 376 carb. 1.1/16" with 260 main jet. 3.5 throttle slide. Needle position 3 (richest)

I have a concentric 928 carb. 28mm (>1.1/16) with 260 main jet. 3.5 throttle slide.  Needle position 1 (weakest).
This gives a smooth run all the way to 60mph where it seemingly stops as if on a limited. Raising the needle does not improve it only makes pick up notch. Increasing main jet makes it cough at full throttle. Decreasing main jet lowers the speed  'limit'.

So I fitted new valve springs.
Old ones were 3-5mm shorter than the new ones so I had hope...
Not so. Made no difference at all to anything
Still powers happily to 60mph the hits a brick wall.

[EDDIE SIMPSON]

I had similar problems on an a10. If you haven't reached top you are still on needle jet settings. On my a10 I used a smaller needle jet and now reaches top. I still have to set up the main jet forsustained high speed cruising.

[paulm]

Ring up Amal they are very helpful and have all the info you require, I have a 628 on one of my B33s and I just rang them up

Regard

[idie]

Are you suffering from fuel starvation? If the filter in the tank above the tap is blocked it won't pass enough fuel for the engines needs as the speed increases. If your tank has two taps try running with both open.

[daveysprocket]

I shall follow your thread with interest, as I've just found that my B33 has a 1" monobloc carb (should be 1 1/6"). All other parts to spec.
As Paulm suggests it's probably a good idea to phone AMAL. I shall try this first and let you know what they say.
Regards.
Dave

[daveysprocket]

Hi again, I spoke to Burlen / Amal technical and very helpful they were too. It turns out that the choke diameter should match the inlet duct diameter ideally. The inlet on my bike is 1 1/8" dia. (pre 1954 size) and it should be a pre-monobloc carb although a 1 1/8" monobloc can be jetted to suit.
My bike was running rich at plodding speeds, this will probably be why.

Regards.
Dave