surging and knocking/ rebuild or not

[carolina]

1990 Yamaha 200hp that I had carb problems with and water in gas tank. Carbs were supposedly rebuilt and I drained 70 gallons of water contaminated fuel. Ran fine on the hose, idled well and no problems but when I put it in the water it started knocking somewhat loudly and surging after about 3000 rpm. Now the surging is worse, all the time, and the knocking/slapping is really bad. Is this probably piston slap since it is definitely from inside the engine? If it is does this mean it will probably need a rebuild? More than a little concerned about putting a lot of money into rebuilding a 20 year old motor. Maybe go to a 4 stoke instead.

Thanks in advance for your knowledgable input.

[jb123]

check comp yet ???

[carolina]

all are ok and fairly close to each other.

[carolina]

Rebuild needed?

Please help here. thanks

[99yam40]

could you be talking about running lean and need to clean carbs again, or the fuel is old and lost octane and burning to fast causing knock

Hard to tell from here

[jb123]

all are ok and fairly close... if you want help we need details

[carolina]

more info

compression is between 125 and 130 on all six cylinders. carbs are a problem for sure but can they make the engine sound like this. ran fine on muffs two weeks ago.

[carolina]

your thoughts please

[99yam40]

Knocking/slapping could be a piston, but the compression is still good, so maybe lost a piece of skirt?
Could be rod bearing.
only way I know to find out is open it up and look