I bought a used tt extra from a guy who is a wiz at fun-flys and rc. It has an OS61SF which has caused me (and I assume him) a lot of grief. It refuses to run rich enough. He had apparently cut off the nedle valve to increase fuel flow. He had flipped the fork which adjusts the mixture with an eccentric screw (also to get richer or leaner- I can't remember which way it was turned). I fixed these, but continued the mixture problems. I finally realized it was rich then got leaner after 1/2 tank and always died (of choking) in spins. I pulled the tank. The fuel supply brass tube was all cracked with tiny hairline cracks at the bend. Sucked fuel with full tank- got lean at 1/2 tank- drowned in fuel nose down in spins. The brass tube looked rotten. When I flexed it, it split all apart. I am fairly new, and have never seen an engine run long enough for the tank lines to corrode like this before.
Tom