Go with an '05 and up. I personally hate the mikuni BSR carb. I double the comment about swapping to a fcr carb if your looking to mod it. Stock, the bsr is fine.  Keep an eye on intake valves too. They have been known to get tight and start cupping.  Other than that lil stuff, they are great trail quads. I have been wrenchin on my buddies 05 since it was new and its been a very relaible and fun bike.