I second Malcom's recommendation. Consider that most motorcycle critical welds are done using GTAW (TIG). GMAW (MIG) works fine, too, and may be the right choice for you, as the learning curve is very short, and there is considerable versatility in what you can weld in the thinner stuff.
If training just isn't available to you, check into some of the manufacturer-sponsored boards. Ther's plenty of help available on www.hobartwelders.com/mboard/ or www.millermotorsports.com/mboard/
hank