mullinsc39,

I take it that this is on a test stand or the plane and you haven't flown it yet? With my experience these little gassers get pretty hot and they don't like it. Running the engine on the ground it doen't give the prop a chance to unload and you could be running it a little lean maybe. I have the Brillelli 26cc and had the 25cc and mine will not transition as well as it should if it gets to hot like on some of the hot muggy days we have had with the temp. at 102 and the humidty at 98%.