I've got the same motor/muffler setup as you. As the weather warmed up I noticed lack of power after being in the air a few minutes.
Checked the head temp after landing and it was HOT! Way hot. Even with the baffle in the cowl and the vent at the bottom, it was over heating. I opened up the cowl around the landing gear even more and started running the motor richer. That cooled it off enough. The days have not gotten 'hot' here yet so there still may be heat problems in store for me. Me thinks I'll be carving around that gear opening even more!

Good luck!


Chip W. (wing still ain't broke... . . . ! No worries. I jinxed it several posts back! Still flying)