As far as my little knowledge is concerned LA AX FX are the version names which released by O.S in a period of time. LA is light powerful series than AX or FX. I have heard a lot of admiration about O.S but never had a chance to use it. My next engine would be O.S. , super tigre, thunder tiger and GMS. Saito is the choice for 4 stroke.

Regards

Mody