yzfrider

I have a 2001 yzf 600r that I purchased new. The bike has about 27.000 miles on it. It bucks and surges real bad about 3500 rpm, but free revs just fine. It has a k&n air filter on it, and a scorpion exhaust pipe. I recently rejetted it with a dynojet kit, b/c the shop that worked on it drilled the jets instead of putting the kit they sold me in it. Still the problem exists. I have cleaned the carbs at least 3 times. The ignition coils test fine. I even tried a spare cdi box and have the same problem. I did take the bike down to be repainted but it was doing this before it was taken apart. I also replaced the notorious 2nd gear about a year ago. The tach also jumps around to 8000 rpm, and if im understanding correctly that has something to do with the fuel sending unit and not a run issue? If anyone can help with this frustrating problem it would be much appreciated!! Thanks, Jeremy