I have a Saito .72 in my Funtana and noticed it progressively became harder to tune, I would hover and hold it there for a bit and it would start losing power and backing down, even when I pushed it wide open. Land, re-tach it and tune it, to see that it was still on and ran fine on the ground, but after in the air for about 2 minutes if I pull vert it would go up about 100 ft then start surging, then start falling off all together, no matter what I did with the needles. Valves tight, fresh fuel, inline filters and all. Well, I found while touching the low speed needle it would change the rpm... not turning it, just touch it. Come to find out the little spring loaded screw that holds the carb throat barrel in had vibrated out about 10 turns and while wide open I could slide the barrel back and forth about an 1/8" in the carb body because of it... moving the mixture tube over the squirter and changing the mixture. While wide open, once the engine is hot the barrel lossens up a touch more and slides in and out with the vibrations of WOT and cause the surging... then it would load up and the vibrations would slow down and it would stop moving in and out and just stay out now, exposing too much needle and fall off to about 5000rpm until you pulled it back to idle, push it wide open and start over again. This baffled me for weeks and finally figured it out so I thought I would post it in case it may save somebody else the frustration sometime Was just about ready to order a new .91 for it!