Could you give us some more information? Tell us what it is and/or isn't doing and many here can tell you what to check and how to fix it.
Check with where you got the motor from, first off. If it's a new motor that doesn't work that'd be where I'd go first. I had one right out of the box that just wouldn't work, and others that were fine. Otherwise, I've read good things here about some dealers (in the sidebars), and Sick Bike Parts and Thats Dax seem to be a step or two above some others.