hello friends.i put an asp 61 fs aron my piper j3 with floats(1800mm,3.4kg) and doesn't have power to make loop(engine not break in but i don't think so big difference in power after break in).an asp fs 70 ar will have big difference?i don't want to make it overpowered(don't want big engine).what do you think(i fly only from the sea)?

A Cub with that weight and wingspan would do better with a .70 four stroke but not a lot. It would mostlikely be sufficient for 'mild' aerobatics like stall turns, rolls and the typical 'Cub loop' which usually turns out to be egg shaped rather than round. However, before you change engines, try entering your loop with a slight dive to build up speed prior to pulling up elevator to attempt a loop. This small amoung of 'energy management' should help you out.

I have a Cub on floats that is 1950 mm or 77 in and felt my OS 55 was underpowered. I kept having trouble with the engine not running. Carb problem because it does not stay running. So I am currently installing a Fox 74, which is just a brute of an engine.