My machine had a very loud rattling sound coming from what appeared to be the jug. I had recently rebuilt the carb and this is the first time I ever really got to hear it run since I bought it. I pulled the head off and there is thick carbon build up on the piston and the cylinder ports. The bearing seemed fine though, the piston had no noticable play. I assume it's carboned up from the old carb running poorly. Does anyone have any ideas as to where this piston slapping noise was coming from? I suppose I really should decarbon it and put new rings in while I have it apart?

 

It is usually piston slap from the lower part of the piston. In time the piston skirt will break. Of course when ours did this it broke the bottom of the engine case as well so it was an expensive fix. I would at least change the rings and when you have the cylinder off check the play in the piston.

 

That sounds good. I brought the piston and cylinder into the machinest Friday to have him look at it. Don't wanna wind up with a broken bottom end. Thanks.