You'll probably get a better response at a vintage sportbike specific site, but I'll give you my quick opinion, as I owned one of those beast motors at one time.
The Z1 is very touchy to having a clean intake. Make sure your breather is clean. You may even want to make a change to four seperate intakes.
Take the carb off and set the float heights. You'll need a good manual.
I would mount up new jets of the same size first. Yours may be varnished up.
Then I would get a good vacuum gauge and balance out the carbs.
I know the advise I'm giving seems backwards, but you need to start out with the carb proper before going further, ie...jetting changes, etc.
The Z-1 is by far one of the best engines Kaw made in that decade.