I have a 1998 Sky Supreme with a Merc 350 EFI. I have a problem when the boat is cold it bogs down and only goes a few miles per hour and i have to play with the throttle to keep it from dying. Once it warms up after 5 or so minutes of putting around it seems fine. What could it be? where would you start? fuel filter, plugs, O2 sensor (if they exist on the boat) any tips would be appreciated.
Fuel filter should be replaced once a year. Fuel pump, coolant temp sensor aka ECT, throttle position sensor aka TPS, along with other sensors and simple things that can be hard to diagnose like bad gas.
Well depending on the boat it could have two fuel filters. You will have a fuel/water separator then sometimes another one on the feed line out of the tank.
The sensors Peter is referring to also can be the culprit. TPS, and Idle air are the ones I would check first but you need a voltage tester. (a cheap one from a auto parts store will work)
The problem now is trying to figure out what the correct sweep and settings for these two parts, I'd suggest looking for a shop manual on that motor.