I had basically the same problem with a G26---would idle all day on the ground---ran great in the air under load---but on a long landing approach with throttle back to idle & the prop "Windmilling" the engine above idle RPM's it would quit every time at just about touchdown! (although no raw fuel out the vent)---restart it & it would idle all day---the answer for mine was to richen the low speed mixture, I guess not enough fuel in the circuit to handle the "Windmilling"---for what it's worth..........