I had similar experiences running and breaking in this engine. It was a breeze, one of the nicest engines I have ever run in. Nice smooth idle, good transition. I installed a Keleo collector ring exhaust on mine too, what a great deep Harley sound at idle! My fuel tank is centered with the carb, and when I hand flip the prop, I immediately see gas flowing through the line to engine. If your fuel tank is lower than the carb, you might try holding the tail up level whilst turning over the propellor to prime( ignition off) This brings the fuel supply more level with carb, and once wet, it should start.