Ive got an old 73 ironhead sportster. When I try to start it, the solenoid just clicks. I pulled the plugs and the engine will then turn over but very slow. I tried bypassing the positive wiring by jumpering it with a jumber cable and it still does not crank with the spark plugs in. I have pulled the stater housing and starter. The contacts are pretty clean and the armature is very clean. The starter gear is in good shape, no messed up teeth or bent engaugement arm or any visible problems. I have a new fully charged battery at 12.9 v. Not sure what else to check. If i bypass the solenoid and jump the starter it turns very freely. I have wrenched on plenty of cars but am new to these ironheads, any help would be great.

 

You need to have an auto electric shop check the windings in the starter. They can check the armature and windings for an internal short. Sound like its shorted.
-sonnie

 

How old is that battery ?