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BSA M21 carb

Hello. Can anyone tell me what the correct carb is for a 1939 M21? I just purchased a bike that is fitted with a 76/014 with a 1 inch bore, 107 main jet and 160 needle jet. The inlet port on the bike measures 1 1/8 inch so is this carb 'strangling' the engine?

The carb needs a rebuild as it’s very worn so I need to know if this can be made to work or if I should be looking for a different model (bore) carb.

Re: BSA M21 carb

The factory fitted the 1 1/8" carb to the M21.. with a 1" carb on the M20.

As a practical matter, the difference in performance should be small, unless you are flat out most of the time...bike might actually be more tractable to ride pottering about at low speeds, but to bring the bike up to factory spec, you should have the larger bore carb on your M21.

email (option): teladelujo@msn.com

Re: BSA M21 carb

Gerard. I'm not sure on the spec for a 1939 carb. It could well be a model 76.
The spec for 1940-45 ex WD is 276P/1B (1B is the float bowl) 160 main jet,106 needle jet. All M21's have a 1 1/16" bore. Ron

email (option): ronpier@talk21.com

Re: BSA M21 carb

Thanks Ron. I don't suppose you know which throttle slide and jet block are the correct ones for a M21?

Re: BSA M21 carb

Gerard, I think the jet block is a standard item for a 276 carb. But here is the relevant page from the latest catalogue given to me last week by Amal.
You should be able to copy it from here....or email me for a copy. Ron

Photobucket

email (option): ronpier@talk21.com

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