I'm with Uncle Pete on this one. My GT6 has HS4 and since I balanced and set the mix with a colourtune they have needed no adjustments at all in several thousand miles. Meanwhile, my Sixfire had HS6 and ran a lot better after I changed them for a pair of Strombergs. Since then, I have had several issues with the dreaded rubber slivers blocking the float needles. Ultimately, I replaced all of the rubber pipe with Gates Barricade, drained the tank (filtered the fuel and used it in the wife's Jazz) and stripped the carbs again. Rubber slivers everywhere! New fuel filters added, one before and one after the fuel pump. I'm hoping this will have resolved the issue.
I can't remember which needles are fitted in the HS4s but could take a look and let you know if you think it would help. Let me know... Incidentally, I have cheap (Ebay) pancake air filters on the GT6. They seem to do the job very well.