I have an older (early 90's) Yamaha 9.9 4 stroke which was running fine last year. I winterized using normal procedures: drained and replaced lower case lubricant, drained oil and cleaned filter, sprayed fogging oil into cylinders and replaced spark plugs. Yesterday I refilled the oil, installed it onto the boat and started it up. It started without too much difficulty, but there was considerably more smoke than usual. I figured this was due to the fogging oil being burned off, or perhaps some of the new oil getting into the cylinders while putting it onto the boat. I left it running for a few minutes, at which time it smoothed out and seemed to be running normally. When it had warmed up some I revved it up to burn off any remaining residues. After a few minutes of this (going up and then back to idle) the RPM's dropped suddenly and I started hearing a "clacking" sound. It returned immediately to normal speed, but even at idle this sound continued, so I shut down the motor.<br /><br />Is the condition obvious from my description? In my experience with gas engines this likely means something like a stuck valve or even a popped piston head. Any suggestions on how I should follow up, other than taking it to a qualified outboard mechanic?<br /><br />Ram
<br /><br />Might you have been running out of gas? The fuel pump will clatter something awful if it starts pumping air.