I have a 2000 cbr600f4 it runs smoothly in low rpm but when it gets up to about 5000 rpm it shudders for a second then picks up anyone know what this could be is it the jets?

 

that sounds like what most people would describe as a "flat spot" in the throttle. when is the last time you changed your air filter? how do your spark plugs look?

 

The air filter looks good still i changed the spark plugs but they were not the same brand they were cheaper spark plugs would it effect it that much ?

 

did you start having the problem after you changed the spark plugs? or did you change the plugs to hopefully fix the problem? I'm leaning towards carbs.

 

There is mid-range reversion phenomenon from Helmholz resonance in intake (pressure-pulses moving in and out of engine). In mid-range at certain RPMs that actually pushes air backwards out of intake. This causes triple-caburetion of fuel, once on way in, once reversion pulse goes out, and another time when that same air goes back in. Resulting in way too much petrol and you get stumble.

You can test this by leaning out mid-range mixtures slightly by shimming needles up with one washer. If it improves, then that’s problem.

 

wouldn't shimming the needles up richen the mixture?