Quote:

"...racing a 2-stroke is considers a big dissadvantage as 4-strokes have found ways to save alot of weight while turning that massive ..."

Without the following rules I’m afraid the four stroke bikes would be less than competitive.

From the AMA website. (motorcycle):
Nationally recognized amateur motocross classes for 2008 will include:
 MX Lites (100cc-153cc 2-stroke/151cc-250cc 4-stroke)
 125 Class (86cc-125cc 2-stroke only)
 Motocross (154cc-285cc 2-stroke/251cc-450cc 4-stroke)
 250 Class (126cc-250cc 2-stroke only)
 Open (251cc-500cc 2-stroke/390cc-650cc 4-stroke)