Bikes recently developed a problem with gear changing. It's on an Evo with a five speed box.

Clunks into first gear OK, I take off then it doesn't want to change up to second, seems the lever wont budge until I power off with the clutch still engaged, then I can click it out of first and then (using the clutch), go to second gear and so on. Usually only a problem with the first change, although a couple of times it's been hard to get to second a couple of times, but only ever very soon after starting out. 

After a few minutes or so, the problem never recurs, even after a longish lunch stop.

Seems to me a clutch problem, and if so, why only at the very beginning of the day? Or what else does anyone think?

Check the clutch adjustment first down in the primary, when was the last time box and primary had a oil change ?

+1 to what Perthhog said. Plus, what year? Is it the ball and ramp or finger activation on the right side of the tranny?