So I have an 04 700 xc sp - was out this weekend and noticed that when got up to speed gradually I could get up to 80mph + no probelm - then in the last little bit of throttle to the bar the engine would slowly loose power and start to slow down.Now if I ease it to the bar from 80 it does pick up speed but if I pin it - it looses power..
I have 2103 miles on the sled - just cleaned the ves valves - mint - compression test was fine - it idles perfect and the power up to 80 is perfect - just the last little bit on the bar is crap! The belt looks ok...
I am fairly new to sledding so if anybody could throw me some ideas it would help.
Thanks.....

Check to make sure rpm's are 8000 min. If less you probably have exhaust valves that require service including bellows.

Search for many posts on cleaning VES and bellow replacement.

If it was warm out, that could be telling you that the main jet is too rich. Letting off slightly will put the needle down, and it will run leaner.

Check your wash at wot as pockets suggested and then check your VES bellows. The '04 should have the updated orange colored bellows (I think) which I have not heard of anyone having problems with so probably not, but if they are the blue ones I'll bet that is your problem. I had similar simptoms when the bellows (blue ones) went on my '03 at 2500 miles.

Thanks for your reply's, the problem was 2 things...
1st - some water in the carb bowls from storage - drained and cleaned both carbs and found the water
2nd - small vaccumm hose from the top of the carb to the air box (small screw in plastic fitting) the plastic fitting was broken off and the one hose was hanging down..

After repaired both these problems took for a test ride last night - It is a new machine, can barely stay on it now!

Happy trails....Snow is here!