I have an o1 Roadking classic, latley have had more vibration than normal, checked out all the mounts and other things that you might with no luck, but changed the spark plugs and it seemed to smooth out for a while.
Bike has 522500 in mileage and I wonder if plug wires could cause a problem like this.
Most of the vibration is at lower RPM then smooths out at higher RPM
Also plug color indicates its running rich

 

with that kind of milage it could be anything....but, if you bike had lets say 52,250 miles, without knowing anything else,yes, I would ohm the spark wires, then check the compression..then buy a can of sea foam, dump it in the gas tank and give it good drive and see if it improves....it could be that the injectors are dirty and you are not getting a good spray pattern out of them...

 

The MM fuel injection has known problems with age and dirt. A good cleaning is in order.

 

Agreed - If the Seafoam doesn't clear it up most likely the Fuel Injection System which is Magnettit Merelli, known for problems. Fouled plugs is rich AFR, hopefully just a dripping Injector....