I had this problem too. To test the starter, jump the two electrical connections on the starter itself with some wire,, if your contacts in the starter are good, then it will crank (as noted, be in neutral).

In my case, the starter was fine, but my battery connection was corroded. Right where the starter cable bolts to the battery. Could also be loose conections on the battery.

-Scerb

http://www.scerbfab.com/carb_faq.html