Try polishing your tip, that may help a little and a drop or two of glycerin or another wetting agent in your mix will help keep it a bit wetter. Also is it hot where you paint, that doesn't help, a lot of peeps forget that most paints temp range is important to its sprayability so really hot or really cold can create issues, also due to the way the air can really heat up from your compressor, if it hasnt got the chance to cool by the time it gets to the airbrush it can help dry paint faster on your tip..Finally try not to stop too often, when we stop our inkflow we naturally continue our airflow, continuing that air flow for awhile will dry any paint on the tip, by reducing the amount you stop, can help reduce tip issues as that. Alternatively when such is happening and you'e tried everything else, add a few more PSI to assist in pushing the paint through, if using low PSI you may find that any buildup causes an issue, at higher PSI it often just pushes through. Or as mentioned, try a different paint, some brands do have additives to assist though personally never needed such..Good luck and hope you sort it..