Hi.
I am restoring a 1946 B31 and can't stop it running very rich on the original type 276 Amal carburettor. I am considering fitting a 376 Amal as fitted to 1955 B31's. As I am a speedo in tank model does anyone know if the monobloc will physically fit on my bike and in particular, will there be enough headroom for the 376 carb. Thanks.
I know that it is a different model. My 1949 M33 runs a 376 monobloc instead of a 276 no problems with clearance.
Thanks for your reply. I know the petrol tanks will be different on our bikes but I don't know if mine sits nearer to the carb than yours.
I'm running a 1948 B32 with a 376 Monobloc and no clearance problems. I had a 1947 B31 with a speedo mounted tank years ago and I'm pretty sure that the tanks are same dimensions apart from the speedo aperture which is well away from the carb anyway. I'm sure you won't have any clearance problems.
Thanks Derek. The 376 /2 1" Monobloc was first used on a B31 in 1955. It had a 260 Main Jet whereas my 276 pre monobloc has a 150 main jet. Do you think I would need to reduce the main jet size on the monobloc?
No! Different design of carb. Try to run on a smaller jet risks damaging the piston and loss of performance.
Stick with the 260, that's the standards jet for that carburator. The engine is just the same from 1946 to 1959.
Thanks very much to everyone for your advice.