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BSA 600cc carburettor

Hi All,

I'm building a 600cc engine for my BSA. The carburettor i got with the bike is an amal 276/410R from a Triumph 5t (bore is 15/16").
The bore is smaller then the standard M20 bore, so i don't think this will work.
Ideally, what bore and jet size should i get for a 600cc engine?

Regards,
Niek

email (option): niek.baecke@telenet.be

Re: BSA 600cc carburettor

An M21 carb has a 1 1/16" bore and a 160 main jet. Amal number for WD M21 = 276P/1B.

Ron

email (option): ronpier@talk21.com

Re: BSA 600cc carburettor

Thanks for the fast reply Ron.

Regards,
Niek

email (option): niek.baecke@telenet.be

Re: BSA 600cc carburettor

Ron is right, but that carb number is for a post war M21.

Pre war and early war time M21's had a carb stamped with the number: 276/024R.

The carb's are identical.

Regards,
Bastiaan

email (option): wdmotorcycles@gmail.com

Re: BSA 600cc carburettor

The number I quoted is from the 1940 Amal book for WD M21 1940-45. The 39 book quotes a 76 carb. Is there anyone who understands Amal numbering?? Ron

email (option): ronpier@talk21.com

Re: BSA 600cc carburettor

That is strange Ron. I know that the Dutch Army M21's were fitted with a 276/024r, that is the 'export' model.

The 'home' model is indeed a 76/024 carb.

This can be found in the 1939 partslist.

I have to take a look in the 1940 partslist for that other number.

Regards,
Bastiaan

email (option): wdmotorcycles@gmail.com

Re: BSA 600cc carburettor

I have just checked the BSA 1940 partslist and in there the 276/024r is still mentioned on page 95.

Regards,
Bastiaan

email (option): wdmotorcycles@gmail.com

Re: BSA 600cc carburettor

Were there any 'WD M21' built as such, or were they simply civilian WM21s ? Pre-war civilian bikes used the 76 with external pilot air.

For 1938, the civilian M20 had the 76/014 body and the M21 had the 76/024. There was nothing in this code to indicate settings or float chamber and the bodies were marked with these numbers.

The WD M20 had the 276/014R body (the R indicating the large single pilot air entry with the openened out inlet throat).

In 1941, Amal went over to a new system including two letters which indicated special features and which float chamber was fitted...The 'bare' body was then given a new number. This means that there can be three or four different 'correct' numbers stamped on the body of a WD motorcycle carb.

For Norton, this was 276/011 (Body or complete carb), 276/406 (spare body only), 276A/1DJ (Complete carb supplied with double banjo float chamber) or 276AE/1BE (Complete carb supplied with single banjo).

It seems likely that the BSA carbs followed a similar pattern.

Re: BSA 600cc carburettor

There were 211 or 212 'WD M21's' build. These were in fact undelivered Dutch Army WM21's which were sold to the UK War Office. Delivery was not possible anymore because The Netherlands were already occupied in that time. The WD M21's were part of contract C7370, delivered between 30/05 and 10/06/1940. On the keycard of this contract the M21's are described as '600 CC Dutch pattern'. These M21's were completely up to the standard of the Dutch state company 'Artillerie Inrichtingen'. I have added a few well known photo of these M21's in British service.

I agree with Rik's suggestion that BSA followed a similar pattern as to the numbering of the carb's. The new number (276P/1B) was only visible on carb's fitted to post war M21's as to my knowledge there were no M21's delivered to the War Office between 1941 and 1945.

C4192169-former-Dutch-Army

London-Irish-motor-cycle-couriers-photographed-one-winter-during-the-period-1939-41

Regards,
Bastiaan

email (option): wdmotorcycles@gmail.com

Re: BSA 600cc carburettor

Amal part numbers: Amal made carburettors with several holes in the body in their 76 series. After spotting the competition in possibly the 1938 six days trials event in Germany, (there was an article in I believe the Blue one titled: "Look, no holes", published in 1939) that an aircleaner would be useful, and that in order to make that possible, the design had to be changed± hence the new 1939 276 series with no external holes.

Parts had Amal numbers on. When a carburettor was built to a specific make and model, the Amal part number would be omitted and replaced with this spec number, eg. for BSA WD M20 that would be the 276C-1B.
276: new body without the external holes, and with the size 6 throtle valve
C: throttle valve, needle jet and mixing chamber for this specified make and model
1B: float chamber of this specification.

The Amal list gives details of the part numebers. I do a repro: 40AM1 AMAL Carburettor settings (154 p.) A4 1940-1968 € 25,20 (excl. P&P)

Re: BSA 600cc carburettor

Hi bastiaan

The war office may not have taken M21 but in addition to the Dutch contracts - 15 x WM21 were ordered in September 1939 & delivered to Dublin in August ( I think) in 1940

Br
Job

email (option): jonnyob1@googlemail.com

Re: BSA 600cc carburettor

thanks all, know what to look for now.

regards,
Niek

email (option): niek.baecke@telenet.be

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