Best estimate was 1978-1980 (just when I was starting school, while living in Japan). The male protagonist (teen?) would jump off of a cliff, punch his fists together, and spin forward in a tight curl.
To my anglicized ears, it sounded like he said "punchu cheezu" at this point and he transformed into a robot head. A female (sister? Girlfriend?) would fly up in some sort of craft and fire out the rest of the robot's parts from her aircraft.
I don't even know if it was in English, but at that age I didn't care. My sister and I just called the show punch-u cheezu.
Anyone remember this one?