MJ's Blown Piston

[Geekie1]

MJ, I was expecting a hole in the piston!! Could be a broken ring, however, I think that the most likely problem is a bad reed. Running lean can cause a reed to burn up which would also give you zero compression on that cylinder. You can check the reeds by pulling the center carb and look down the manifold barrels to check the reeds on the bad cylinder and comparing them to the good cylinder next to it. To get a better view and a little more work, you can instead pull the intake manifold with the three carbs still bolted to it. You will need to disconnect the fuel lines to the carbs, oil lines to the manifold, disconnect the carb linkages, not a difficult job. If the reeds are damaged, you will definitely see it when you pull the manifold, carbs, reed as a unit!! Reeds perform a similar function as valves on a 4-stroke. To repair the reeds is a job in the lower hundreds of $. The cylinder wall does look a little screwed up though so some work on that cylinder will probably be necessary. If the reeds look good, you most probably do have a broken ring. Yamaha oil fuel/oil is not mixed in the carb but in the intake manifold. I think the oil system on the Yammie is pretty simple and bullet-proof. If the oil level sensor lights on the helm instruments is working (self test when starting) and if you get low in the main tank or the small tank on the engine, you should get a yellow or red light and the rpm's of the engine will drop to 2000rpm. There is an article in Bass and Walleye magazine that explains the whole thing. Monday I will post the URL that has the article. Although an oil pump could fail, I have never heard of one failing on a Yamaha. But I guess I haven't heard of alot of things.