You should clean them after 500 miles after the sled is new (at least). You break the sled in on the "blue" oil and that leaves carbon deposits. After you first tank of oil when you burn the synthetic, you shouldn't have much of a problem. Just check them every 1000 miles and see how they are.
Are you sure the 600's are all stock? My 02 600 with some clutch work will beat a stock 800 quite badly. The 800 out of the box turns too high rpm and dont make that much more power than a 600 at 8200 rpm or higher.
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