I guess you guys are right. The oil was kind of black, with a gray tint to it. It also wasn't clear. It was more like a paint. It was light the first couple of flights, then it turned dark. I thought I trashed my engine. I have tightened the muffler as tight as I dare. I have broken that long screw before on other engines. The nut and screw are both tight when checking. Thanks for the help.