Every 2 or 3 three starts I have this problem: The engine will run very slowly, and at the same speed, from idle to 1/4 throttle. If I advance beyond 1/4 throttle, the engine will quit. On the next start, however, it will usually run normally.

Also, on some of my preflights, when I put the plane verticle at WOT, the engine quits. Other times it does not. Any help would be much appreciated. Thank you.