bringing back an 82

Just tore down and rebuilt an 82 kz1000. Everything is wired and put back correctly, carbs cleaned and new gaskets, oil, seals, plugs, wires. Turn the key and all I get is this chug chug chug chug like the starter doesn't have enough power. It is getting voltage, the starter clutch is fine. The owner of the bike said it ran before storage. Could it just be a bad starter? How can I check it out? Any and all help is greatly appreciated.

Check the battery voltage during starting.
If the voltage drops below 12 it is most
likely the battery.If the voltage is ok
the connections between the battery and starter
may need cleaning or replacing,this includes the
starter relay.If you jumperwire a fresh battery
straight to the starter and still have a slow
turnover I would replace the starter motor.

I would check the voltages as was recommended.. then try jumpering the starter relay. It's like the old Ford models where you can almost do it with a screwdriver across the two large terminals. Use a good jumper cable though and be careful for any spilled fuel as this makes a big spark.

I had the same problem with a 82 KZ1100.
I took the starter apart and found carbon dust (from the brushes) everywhere.
I cleaned it well, and used emory paper to polish the commutator.
Now it starts great!

i have a brush kit i bought from z1enterprises for my 82 kawasaki csr 1000J unused in its container, turns out someone stuck a cop starter in my bike at some point in time.

i only want 10$ + shipping if you need one