My 2004 Adventure has the same problem. New fully charged battery or jump start makes no difference - starter spins, but the starter gears never engage.
Originally Posted by Weekend Hack
Thanks for the help...
I looked at that as a problem but the rotor was well secured. So the problem was the starter was spinning backwards! There is a small o-ring that holds the positive post off the case of the starter. I assume the pressure from the positive starter wire squeezed the o-ring until the positive side touched the case making it run in reverse. Trip to the hardware store and .29 cent o-ring and it started like a champ.
Where is the o-ring, that allowed the positive post to ground out to the case? Inside the starter, or outside?
I've got two posts on the rear (bike's right) side of the starter. Neither has an o-ring. Disconnecting the rearmost (ground?) made no difference. Disconnecting the forward post cut off all electricity - turning on the key = no lights, no cranking, no nothing.