baja mercury 120hp sport jet allergic to water

[unhappycamper]

I have a 1995 mercury sportjet. It has recently had all pistions and rings replaced + all four cyclinders bored out. It starts fine out of the water but starts and dies when in the water. It sounds perfect out but dies when given throttle in the water. The engine was recently timed. Hope for some needed advice to what may be causing my grief.