BSA M20 (I Think)

[Andy_G]

Hi all, just a quick question...a relative of mine has a 500cc single BSA Side Valve. I think it's an M20 with a  tank mounted speedo? The bike was not military. It needs the mag setting up correctly as it kicks back on starting and doesn't run quite right, tends to pop and backfire a bit. Once I have established the model. I'll ask about setting up the magneto.

[L.A.B.]

The engine and frame numbers should identify it?:

You can check them here:
http://www.bsaoc.demon.co.uk/intro.htm

Under the heading:

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".....yearly listing of all engine and frame numbers,

Years up to 1920All models up until 1920

1921 to 1930All models from 1921 until 1930

1931 to 1940All models from 1931 until 1940

1941 to 1950All models from 1941 until 1950

1951 to 1960All models from 1951 until 1960

Post 1960All models from 1960 until the factory closure in 1973."

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Any information about the type of magneto will probably be useful too?