Hi guys,

I just bought this bike last weekend and took it riding thursday night- it had rained during the day so there was some water and mud on the trails but nothing too serious. I was out riding for an hour when i got stuck in maybe 15" of mud, but the engine was never submerged. I got out of the mud and continued riding for another 10 minutes until as i was going up the hill the bike sputtered and died out. I thought i had run out of gas and filled the tank (I was running on reserve at that point) but with a full tank of gas the engine shuts off when I twist the throttle- any ideas what may have gone wrong with it?

Well, it's tough to say, but I guess I'd start with the gas and the carb.  When you buy a used bike, you also get used gas.  No telling how old that stuff may be.  If you were running on reserve, you were sucking stuff off the bottom of the tank.  Perhaps there was some water in the bottom of the tank that got sucked into the carb, or maybe got some dirt in the carb.

Try it with the choke pulled out. If it runs better, it has a plugged pilot jet. It is tough to clean them, and easy to replace them.

Replace it with a #38, which has a Yamaha part number, and it will run better.