Misfire

[wr400 newbe]

I have a 98 wr400 that acts like a four cylinder that is missing on one cylinder. When I am trail riding I don't notice it that much because I am on and off the throttle so much but on the street cruising at a steady speed it hicups like it didn't fire about once every 1or 2 seconds It doesn't seem to matter if I am at 1/4 or3/4 throttle it acts the same. Any help or ideas would be greatly appreciated.