55hp Mercury Boat wont start when in the water

by Kate
(Illinois)

My husband and I just boat a john boat with a 55hp Merc outboard motor. He cleaned and adjusted the carbs already. He then hooked it up to the hose and ran like a champ. We to it out for the first time today and it wouldnt start. The motor acted like it wanted to, but when he put it in gear, it died. He pulled it out, and it fired up again. So once more he put the boat back in to the lake and its the same problem!!! Help!