So I'm getting the boating itch and want to start thinking of possible solutions to my yamy 150(96 SWS2). First not 100% sure there is a problem just 99.5%. The problem is that this motor really has a shake in gear at low rpms. Its on a whaler outrage 17, and has been like this since I got the boat a couple of years ago. I did a lot last year went through the carbs (twice once I did it once a yamy dealer did it), did comp/leak down test, many sets of plugs and fuel filters, ran on external tank, replaced fuel pumps, shock treated the fuel with ring free, decarbed motor with yamy decarb spray. The problem is worse with a heavy stainless 13.5X18 (OE yamy prop) vs a lighter aluminum prop 14X17(oe yamy also), but can still notice it either way. I was told that the 18p prop was really made for the 150, and it performs the best 50mph at 5200. It also seems a bit like one cyl drops in and out at mid range. Every time I pull plugs they seem a bit wet and pretty much all the same, and some oily sheen in water when running at dock, but not a oil slick (smells like unburned fuel). I picked up a factory SM and want to check a few things, like make sure correct jets in carb (looks like SWS2) have different jets then reg 150. Any thoughts would be helpful. Also when I took it to the dealer they said they had not seen one shake as bad, and the carbs needed overhaul so I let them do it. they said they got it running great, but when I took it out it was the same. I was just $700 lighter.
