New engine and carb. Proving not very reliable.

Newly rebuilt Kawasaki 440a engine with new fuel pump and new mikuni carb. Performs flawlessly for 3 flights and then suddenly on fourth has a sudden loss in power. Made an emergency landing where it quit completely as soon as I pulled the lower back after touching down. Had to push the airplane off the runway. Unable to restart. Not sure what to do. I checked for spark. Seems like it's OK. Been told that fouled plugs sometimes don't spark under compression but I kinda think it something to do with the carb. I guess if new plugs don't make it start right up, that's where I look next. There is a filter immediately before it. Has me concerned. Was running 20:1 for breaking in new engine. Never ran with that high an oil percentage before Any ideas?