Will not go into 6 gear

I have a kz 400 with a engine from 1978. It runs very good. But it wont go into 6 gear. what can be the problem?

I just looked at the parts diagram for a 78 KZ400B at buykawasaki.com, and I only see five gears, so are you sure it's a six speed transmission?

A kz 400-B1 from 1978 has 6 gears.

I just check the bible (AKA www.kz400.com/ ), and you are indeed correct, the 78 was the first year for the six speed trans.

About all I can suggest is to check out www.kz400.com/ and see if that problem has been covered, at least unless the expert (Ibsen2200) stops by.

Yeah, it seems like the 78 400 B had a lot of new stuff.