Ok,tried it all, balsa box, trumpet both facing rearward and forward, no trumpet, leaning needles untill poor performance low end and high end. I have a Quique yak 102" cannister mufflers does the standard bad things. Runs great on the ground, sluggish on takeoff untill turned skyward runs great throughout rightside up and knife edge but turn this baby inverted near 1/2 throttle and starts to loose rpm. Don't move the throttle and roll right side up and goes back to running perfectly. What gives with this engine. BTW I have the new style trumpet with the insert to reduce the opening. Any ideas??????