After my intake modification i have used a 33:1 ratio without any visible issue. But as this engine runs on bronze bushing and not on needle bushing, I prefer to come back to 25:1 (Stihl HP ratio recomendation for a 2 stroke engine X 2)
Note 1: I have removed the cylinder without removing the engine from the plane. It works with the Saito exhaust pipes, but not with the Keleo ring.
Note 2: I have bought a FG61TS and I hope that I will have less fears to put it in a Ziroli AT6...
JM