Check your compression to start should only be 5 pounds different between cylinders. then check timing on each cylinder. Go to each plug and make a mark on the flywheel and number whitch cylinder it is. if timing is off on one or more cylinder this means you have a bad diod. if all good then you must have some dirt in your carbs. Clean with a good marine cleaner like Omc engine tuner NOT reg. carb cleaner, This stuff is junk. Hope this helps
