engines

Hi!! I charger my battery and after the charger is full, i start the engine and Works about 30 seconds and turnoff. In next day, when i tray to start, all is normal, pump, panel, beeps, no erros displaying, but when i try to start, nothing occours! Just the pump starts. The fuses and relays...

Looking for an engine, Mercury Optimax 250 for my 2003 Seadoo Islandia. I would like to replace it with a Rotax engine, but don't know if it's worth it? I would seriously need some guidance on this one by a professional. Anyone with some ideas? Thanks, Rob