I use 0.8mm, so that's not the issue. Either paint viscosity or a gunked-up gun. Do you clean the gun out after every day's use (as well as if you change paint colours)? I run thinners through, then remove the needle and clean that. Also the rotating front nozzle plate and dip that in thinners for a bit to get all the holes clean, and dip the end of the nozzle in thinners as well and wipe that with a cloth.