The pilot of an aerobatic airplane reported experiencing engine roughness while in the traffic pattern; resulting in an immediate return to the departure runway.

Narrative

On short final directed to go around by Tower Controller for traffic on the runway not clearing expeditiously. On applying power; noticed some hesitation and engine roughness. Requested priority handling; turned crosswind then downwind and was cleared to land number one. Executed a precautionary landing without any further issues. Taxied to the run up area and was unable to duplicate the engine hesitation or roughness. Suspect possible spark plug fouling as a consequence of extended downwind and low power setting necessary because of traffic we were following on the arrival and approach. The extended downwind was as instructed by the Tower Controller and flown at A lower power setting than normal cruise; additionally; the base turn was also called by the Tower Controller who felt spacing was adequate; it turned out to be insufficient resulting in him subsequently calling the go around at approx 300' AGL. Because of the engine roughness I decided to request priority handling and land as soon as possible rather than have to fly an extended pattern as there was additional traffic on final that I may have been sequenced behind. I felt the best course of action was to land as soon as practicable.