Starter Motor Sluggish

[Myumi-2]

Ive recently purchased a CB750 K2.  It has been parked and not started for 20 years but generally complete.  After some minor work Ive got the engine running and it starts second kick.  Im now working through the rest of the restoration.

I have however discovered a problem with the starter motor that has me stumped.

When I hit the starter button the starter motor turns over however it is very slow and not sufficient to start the motor and  the starter slows down to a stop in about 3 seconds, after which it hums but does not turn over.  If I hook it up to a more powerfull battery (a car with the engine running) I can get it to start the bike.

Ive replaced the battery.  The solenoid is working.  I do not have any undue resistance in the power cables from battery to starter motor (1 ohm of resistence). I've replaced the brushes and gave the starter motor a clean.

Ive removed the gear cover and had a look in.  There is plenty of oil on the gears and things appear complete.

Any suggestions on where to next would be appreciated.

Thankyou.
 

[Rod_Knockin]

bad starter motor winding.

[BunBrown]

I have the same story/question... When I hit the starter button, the solenoid clicks, headlamp goes dark, but no starter.  I pulled the starter out, it will spin under power but has so little torque, I can stop the shaft rotation with my fingers.  I "assume" the starter needs replacement?

[Re-run]

Well it may not be "bad" so to speak. You will probably want to check it out. the manual should show you what you can do as far as simple repairs. Could be as simple as a brush that is bad or just a bushing.