I have an 04 f-7 that has what feels like a missfire on the buttom end. when I go wot from a stop the sled takes off and then starts to bog slightly and sounds like its missfireing alittle then slowly clears out and begines to smooth out. I just noticed this problem this year when racing my friends rev 800, I used to bet him down the strech but with this happening I cant????? I put now plugs in and no differences, I cleaned the power valves but do not know how to set them. Could there be anything eles.