Seen it a few times, are you running the cams in correctly, ie not too low a speed for first 20 minutes or so ?
Spray bars are faves for getting blocked, Burton's used to do a bar with a filter in it, maybe still do ?
How much is plenty ?, as there should be a defintite strong jet even at idle when warm.
I always used to use regrinds as these were better as they were already work hardened, what cam spec is it ?
tabetha