Hi Folks! I'm new to the forum and I'm looking for help / advice. I just purchased a used (less than 50 hrs) 2018 VX Ltd Waverunner ... runs rough, unable to get RMPs over 5000 on the water (but engine runs fine on lift with hose water cooling). Took to Yamaha dealer service department ... they thought plugs were bad, gas was bad ... changed both but problem persisted. Service guys then reviewed electronic records and discovered that more than a year ago Yamaha declined warranty engine replacement for former owner; claimed engine was ruined because former owner over-filled oil. Dealer estimates cost of total engine replacement around $7,000 (seems like a lot). Can oil over-fill permanently ruin engine? Is there a less expensive repair option? I'm in the Tampa area ... are there qualified non-factory repair folks that can rebuild or replace the engine? Any ideas what to do next? Any / all suggestions appreciated. Thanks!

There sure isn't much info here.....what exactly was/is wrong with it other than runs rough, I mean does it have good compression? Good spark? Good fuel pressure?

Overfill with oil won't do much unless it was way overfull and something like a rod bent. It's just not likely. Anyway, you really need to diagnose it correctly. I've heard stories of dealers doing shit and it sure sounds like a lot of their techs don't know the machines they work on very well.
Check around and see if you can find another shop to look at it, maybe a boat shop that has a water tank.
Also, has anyone checked the impeller? Maybe it's bent or has crap in it. That would make it run bad in the water but not out.

Thank you for the reply. I'll try to be more descriptive about the problem: The engine starts fine and RMPs will slowly rise under light throttle, however, at low / no wake speed it sometimes feels as though it's 'missing'; if more throttle is applied, after choking a bit, RPMs will rise, but never exceed 5000 (top cruising speed of 17-18 MPH). Again, when on a lift with hose attached, engine runs fine and RPMs will go to max (9000?). As for compression and spark . . . the plugs have been replaced, then after an hour of running at or below 5000 RPM, they were pulled (discovered fouled) and cleaned. Also, the fuel was completely drained, fuel lines cleaned and fresh fuel added. I think if it were a fuel issue, the problem would persist whether in the water or on a lift. I agree with your thinking that it's hard to completely ruin an engine by over-filling the oil. I'll have the shop check the impeller . . . I've heard that may cause this type of problem (I don't understand why). Lastly, I'd welcome suggestions about a reputable / qualified mechanic in the Tampa / Clearwater area. Thanks for your help.

In what way were the plugs fouled? Fuel or oil?
it is not surprising that it runs worse on the water simply because it has a real load on it.
Anyway if they were fuel fouled I would say you have a fuel problem of course. Does it blow black smoke? That is a sure sign of too much gas. Have you looked it over real well for any vacuum lines off/broken?
I'm guessing this new of a machine is fuel injected and if so it will have a self diagnosing computer (ECM)
Once you have the basics like confirmed good compression, strong spark down, it will likely need someone with a service manual to fix it. It seems like a dealer that sells these could do it but I'm hearing stories that they seem to be not so great at it.
When something is fuel injected you can't just look at it to fix it, you need a manual and tools specific for it after the basics have been verified good.

Thank you for taking time to reply. The tech at the shop said the plugs were fouled (I personally didn't see them so I don't know if it was fuel or oil). There has never been any black smoke. The shop took a more thorough look at things . . . they said that they looked inside the cylinders with a 'scope' and saw rust . . . they are convinced that it needs a new engine (at significant cost). The engine has so few hours that I can't understand why they can't just rebuild it . . . maybe because it's a timely task the shop doesn't want to bother with rebuilding; dropping a new engine in would be quick 'n easy. I'm thinking about using it as a trade in . . . a dealership would have the time and resources to fix to fix it, and their cost would significantly less. Again, thanks for your help.

OK , I'm going to assume they checked the compression and it's bad. So thus it needs a lot of work. Very few shops rebuild anymore, especially small engines.