RE: How do you remove burnt oil from a 4-stroke muffler ?
All of the above! I gave a few to my nephew-in-law and he glass bead blasted 'em for me. Also sand blasted some myself w/ fine sand @ low pressure. Then I ultra sonic cleaned 'em in alcohol to get the grit out. I think wire wheelin' them works good too, If you don't mind the finish it leaves on 'em...I had this blue liquid for cleaning jewlery that smelled like that home permanant stuff my sis used to use, that came w/ the sonic cleaner, but I can't find it anymore. That stuff would take anything off, inc. rust, but it would leave a gray dis-coloration on alum. parts.