Hunter 29.5 slow to starboard.
First of all, most cruising boats have their knotmeters installed off to one side of the centerline and so tend to read differently from one tack to the other. Beyond that, there may be differences in the jib sheet lead (The block on the track that the jib passes through) from side to side so you may want to check that. Roller furling jibs have heavy sunshields on one side of their jibs. I have seen that change performance from one side of the boat to the other. Other things might be a warped or assymetrical keel or rudder.