Weak hot starting - '82 KZ 750

I have a 1982 KZ-750 E (4 cylinder) that runs great. I am having a
problem with hot starting. When the bike is cold, the starter cranks
the engine over Ok, and the bike starts well. After riding the bike
for a while (10-20 minutes) if I shut the engine off, the starter will
not crank the engine over. It tries to crank, but it just doesn't have
enough power to spin the engine over. The battery is new, and it holds
a charge well, and the charging system checks out Ok. I have 14.5
volts at the battery at 4000 rpm. If I let the engine cool off for a
while, the starter will crank the engine over and the bike will start.
I suspect that my starter is just weak after 26 years of use.
I was just wondering if anybody else has encountered a similar
problem. I am going to try to pick up a used starter at a junkyard, or
possibly pull my starter apart and take a look at the brushes.
Thank You for your help!
Greg

 

The starter (specifically, the starter clutch) on that engine is well-
known for wearing out and/or seizing up over time. It probably needs
to be stripped out and the clutch replaced.

According to the manual, this means splitting the engine cases. In
fact, it can be done with the engine in situ, but you still have to
remove the sump and engine clutch assembly. It's fiddly, but it can be
done.