Start with the basics of any trouble shooting. Do a compression check and spark check. I need the compression numbers on all cylinders. not close but the numbers that you see on the compression dial. First thing you are going to need is a repair manuel and a good spark tester and compression gauge. If you are going to repair one you need the manuel because it will tell you far more then I can. If you don't know which manuel let me know and I'll pm you a link and number where you can obtain one. Best money ever spent. The plugs not fireing can cause one to do this there is a way to check the power pack and the directions are in the manuel. As for the carbs being set togeather they have fixed jets and the only setting you can do is sync. and link. If you susspect the cables then try unhooking them while in the water and shift it manuelly. The power packs can go all at once or intermintly so don't go throwing parts at it until you know what you need. If a person doesn't know what they are adjusting on your motor then tell them to leave it alone because it is your money that will be used to repair it. If one is not running right then find out why don't just make it run fix it.