We can go round and round about the battery until the earth dies and it still won't start if you don't verify the numbers I gave (for a reason), your skills mean nothing if we do not get that clear. A weak start is not battery turning starter slowly, they get even worse, to a click only and starter does nothing or even worse to nothing and not even a click. Yet the lights and other will still seem to work. That absolutely is NOT a check for a good battery.
Please verify the exact battery voltage or we can go no further. Putting it 'on the charger' means nothing as well, we have to have proof that goes past that being we get that every day and the batteries still end up being dead.
Still, assuming battery is good by being new, you can bypass the solenoid to go directly through starter by using a set of pliers to put one handle on a big battery positive cable at the solenoid and the other handle on the other big cable coming out of solenoid to starter and that will make starter spin up but be ready for possible sparks doing it, hurts nothing. That tells you starter solenoid is bad.
No insult intended at all on the above but others read these threads and the most mis-aligned legend of all is that batteries are good if the lights and other come on and it was 'just charged'; thousands if not millions of man-hours are wasted right there. I say that having been there so many times I would die before I quit counting them. Why a give back on the battery volts settles most questions, even new batteries can be bad if the typical Chinese one most commonly bought.
These early DOHC have a major issue with alt rotors that can fail in a 100 different ways, one is to slightly undercharge to drive bike a month until battery gets slightly low enough it then refuses to start right. That rotor fail is the most common failure the bikes do. FYI.
