Hey i have an 04 yz 450f. I've had it since new and never had a single trouble with it. I went and started it the other day and it runs fine in 1st, 2nd, 3rd but you hit 4th and it surges. I put fresh premium in it, cleaned the airfilter and carb. TPS measures to spec. It definatly seems like a fuel problem but i could be wrong. Anyone ever had a problem like this?