Hi, Well for starters the timing could be out of adjustment, or the idle could be set to high, Could be bad gas, Water ect. Check your fuel by pulling the filter and look and smell it to see if it's bad, If not, Then the idle is/was set wrong from new And the dealer may have set it wrong
at new boat prep time and that should be covered because you have all ready paid for that while buying the boat from new It's in the deal of buying the boat and they call it prep and delivery, And you pay for that up front. Also if you have the new turn key start engine then and it is running like that then some times the only fix is a new carb needs to be installed.
There might be a sticker on top of the flame arrester that would tell you what the spec's should be set for. Keep in mind to set the timing you will need to ground out a certin wire to check and adjust the timing. you should get your idle adjusted to spec's first, Because most of the time the 4cy engines are harder to set the idle just right then V6/8 engines because to get it just right you normal have to play with and adjust the throttle cable to get the engine to idle down smooth every time after moving the throttle. It takes some time to get it just right or you could have different idle speeds at times.
