Hi I am new to the BSA M20 scene and just purchased a 1942 M20. I was told that you could get a little extra power out of it by moving to a larger size carburetor. I believe it has a 24mm on it stock and saw that someone said you can move up to the 30mm. I am on the Brit bike forum and said that seemed like a big jump and to ask if anyone here now's if that is correct or what sizeh could I move up to and the model of the amal carburetor that would be.Thank you

email (option): bjsullian23@ymail.com

Hi Barrett..I'm afraid you have been ill advised regarding carb size for the M20...The correct size carb for the M20 should be 1" (25.4mm). There is no real gain in fitting a bigger carb..other features of the engines design effectively prevent any gain from a simple enlargement...The most important thing is to make sure you have the correct carb in good condition, correctly jetted etc.and set up nicely. Also with the M20 make sure the ignition timing has been accurately set at 7/16" before top dead centre (with the adv/rtd lever set in the fully advanced position).
It is important not to run these engines with the ignition set at all retarded during normal use....Ian

email (option): ian@wright52.plus.com