Yamaha ran rough at low rpm

[patrick16]

I just bought a 2004 Advance 257 with twin yamahas with 250 hours. They ran well during trial, but after a short trip recently they were running rough in the no wake areas (vibration).

Any idea what this might be? Suggestions?

 

[ItalianAngler]

Those are some very low hours for a 17 year old boat, it likely sat for long periods with little to no use. My F225's will get a little congested once a year usually, I run injector cleaner and push it to the pins a few times and it will go away. I put the cleaner in my aux tank on a day that i know i will be using all of it. I think they can just get gunk in there that needs blown out, and if yours have been sitting then it wouldn't be surprising in the least. Something to try before getting too into searching for an issue. I have 1800 hours on mine and they run like thoroughbreds.

 

[seasick]

It could be a zillion things but some are more likely that others. First of all, you didn't say if you did any maintenance and if not was any maintenance done on the motors recently. You could have bad gas, perhaps water from sitting. You need to remove and drain filter contents into a clear jar and let it sit for 15 minutes or so.
You should pull and inspect your spark plugs to see if they are fouled or too dry ( no fuel).
You might have unbalanced props or spun hubs. Sometimes that causes shaking and vibration at low speeds, sometimes at higher speeds. In any case take a look at the props for obvious damage. Note that if the props are the issue, the vibrations will be a lot less when the motors are in neutral as opposed to in gear.

In general if two motors started having issues at the same time, I would suspect bad gas first.