BR600 back pack blower, with no compression. Squirted two stroke oil on piston, no change, took the muffler off, could hear air escaping out the exhaust valve. Squirted oil on the valve through the port, compression for a couple cycles and it would wear off. Repeat, the same. So I checked, plenty of lash, so that was not it. Decided to really squirt some oil in it and left for a whole day. Compression was returned. Must have been some carbon or something built up in there pretty good. So I set the valve lash with the little Stihl tool and put back together and ran. blew a little smoke from my oil squirting but ran just fine after that, and I didn't have to tear the entire machine down to get to the end result.