85hp force motor running rough

[Jimbo82]

Bought a 198o bayliner Capri for 700$.The previous owner says boat will do 45.I can only get it to 20.Feels like engine is not running 100%.any ideas.This is my 1st boat.thanks

 

[pnwboat]

You need to check compression, then verify that you have good strong spark on all cylinders.

 

[Jimbo82]

How do I go by doing that sir