You don't need big power, pumps, trim, to do backflips in the surf.. The Wave will do 50% of the flip for you
You need to be 110%, if you puss out its not going to happen... Backflips got to be the easiest trick, but take balls & someone willing to give it 110%...
You have to have the right surf, 3ft + surf with decent faces, you have to plan it right since you don't have brap to plan it late. Try to hit the wave when its almost ready to break or just starting, very fine line there... You gotta hit the wave, 1/4 idle up is not going to work... Once you leave the wave the ski is vertical & the nose will start to come around. Having you butt off the back like your man handling the ski also helps, throw your head back (Look back), this will help the ski come around ... When learning Backflips the head is very important, this helps your body get in the correct position & gets the ski rotating..
Its that simple.. Once you get use to them you can throw harder or Less, body position will change speed of rotation.