What throttle setting are you starting it at? Try it wide open.
I've got 1 Norvel AME .049, 2 AME .061s, 5 BigMig .061s and 3 .074s. I love these little engines.
An APC 6X2 is fine and loads the engine about the same as a 5X3. I agree that a 6X3 is a little too much. The APC 6X2 or 5.7X3 props or a Cox 5X3 prop work well. I break mine in on a test stand with a Tornado 5X3 soft prop which tends to de-pitch and is a fairly light load on the engine. It is also easier on the fingers.