This was a known issue with the 02-04 Sp 700's. Polaris has a retrofit kit for it, to the tune of $500!! I did mine, took me the better part of a day but the quad starts and runs better than ever. I'm not sure if the 600 is in the same boat, but it is very possible. The part number for the kit is 2202603, and most of the online parts houses carry it.
2004 Sportsman 700 - battle tested and proven!
2008 Sportsman 500 EFI - hers
2011 Sportsman 850 XP EPS - the new guy