red hot exhaust

Just acquired a 79 kz 750- got it running after new fuel
and plugs but it's still faltering and one of the exhaust
pipes gets red hot (very visible at nite). Could it be running lean from a bad carb or is it more likely a valve
problem?

check carbs/filter

Would also check ignition timing, and that advancer unit is correctly functioning.

When setting timing, always use the F marks. Ignore the T marks.
See example pictured below.

Good Fortune!

[Click on image to enhance view.]

Wow, that is a big difference in advance curves between the early and later Z1. What changed, the idle-position or the full-advance position?