G,day Luke
My boat is a Quintrex Freedom Sport 460,i've been through the same thing....it drives me insane when im looking forward to a day of fishing and the Yammy starts coughing as soon as i leave the boat ramp.I've tested the fuel filler for leaks and disconnected the breather hoses at the tank and shot water at them with the hose to see if water can get in but....nothing.Because the boat lives outside uncovered i've narrowed it down to either condensation or a pin hole in the top of the tank.To save spoiling a day of fishing...the day before i always disconnect the fuel line at the motor and use the primer to pump fuel into a glass jar to make sure theres pure fuel there,then i remove the fuel filter under the transom and empty the contents into a clear container....theres always water in there without fail.Don't forget to fill the filter with fresh fuel before screwing it back on....this method hasn't failed me yet.....hope this helps
Cheers.Pete