There are some tools specific to large GY6-type engines, but they're pricey and, unfortunately, rather large. I was hoping for something somewhat portable that I could bring with me on Cannonball.
Then I stumbled on a post suggesting a variable-sopeed clutch holder for air conditioners. Only $9. I'd never seen it recommended for scoots before so figured I'd test it out.
http://www.amazon.com/gp/product/B004KE ... 00_s00_i00
Worked like a charm! Short-handled, so required a little oomph to hold in place. But for home use, a pipe on the handle might make things a bit easier.
Best of all, it should work with most scooters. (Possibly not Vespa clutches, but will work on the variators.)
Pics below are for my Helix, but it should work on a Buddy as well. May not fit a socket through the center hole, but as the variator pic shows, you don't have to!




