I had and still have a lot of idling problems on this plane with the OS .26 four stroke, which has an air bleed carb. I can get this engine to tick over reliably at about 2800 rpm on the bench but on the plane, 3500 is about the lowest reliable idle I can achieve. I think the problem is that the fuel tank is below the engine level. Air bleed carbs have very limited fuel draw ability at idle and the idle adjustment gets really tricky if the carb has to lift the fuel any amount. That is why I am considering redoing the engine mount as an inverted mount. It should bring the carb spray bar more in line with the center of the fuel tank. This is really exagerated when the tail wheel is on the ground and the plane sits nose up.