Hey guys, Got a stihl br600 blower that I have been using personally for commercial lawns for about 4 years now. I use 89 octane ethanol free fuel running stihl's HP ultra synthetic oil at 50:1 ratio. The blower started up fine this morning but ran so rough I couldn't use it. The was no indication of problems anywhere- fuel fine, spark fine, compression fine. I finally opened up the spark plug to look at the piston and it looked fine. But what surprised me was that the cylinder sleeve around the piston was also moving up and down. I have never seen anything like this before. Is there some sort of cylinder sleeve around the piston that is suppose to do that?