Is your engine quiting only at idle speed, like when you do a spin or randomly at any time on full or part throttle use?

If it's quiting at idle , try leaning out the idle mixture screw a little screw. If it's quiting at part or full throttle (and you seem to be runing at a rich setting), it might be over heating. A cause of over heating could be insifficient EXIT area in the bottom of the cowl. In order to ensure proper air flow thru the cowl, the air EXIT area has to be between 2 and 3 times the area of the openings at the front of the cowl. Open up the bottom of the cowl w/ a Dremmel sanding drum, if necessary.

One other thing, these pumped engines have to be setup differently from non-pumped fourstrokes. If you check the manual (huh, what manual you say? ), you'll see that OS recommends peaking the engine and pretty much leaving the main needle valve at that setting. The fuel pressure from the pump ensures adequate fuel flow to the engine. If you still want to be conservative, you can run it a little on the rich side of peak rpm, but IMO 1/4 turn is too much.

One final thought, you ARE leaving the tank's vent line unplugged and open to the atmosphere, right? If you aren't that would explain the engine quiting from fuel starvation.

FWIW, I have the same engine with over 100 flights in a hard flying aerobatic plane and it's never quit on me yet.