Today, I have just found myself the new owner of a YM1 Yamaha of 65 vintage. A 305cc 2 stroke twin, of which I know is basically an overbored YDS3.

I know that the oil pump is gear driven and when you pull in the clutch lever the pump stops, (great design eh!) and also that the kickstart gearing is rather weak and was modified in later versions. Apart from that I don't really know anything further on the model.

Is there anyone out there who can provide me with some information on this very rare machine, as I would like to have some history on why Yamaha produced such a bike.

Was it directly in competition with the CB77 of Honda, or did Yamaha produce this machine before Honda uprated the CB72 ?