I have used my BR600 for 4 years without any problems. Because I use it for probably a little over 100 hours a year, I have been checking the valve clearance, then Decoking the engine using the STIHL DeCoke fluid. This last time when I went through this valve and decoke procedure, the valves did not need any adjustment, and I only decoked it using the decoke fluid. When I finished, I ran it for about 20 minutes, and the engine just quit like it ran out of fuel. When I tried to restart it, I found it no longer had any compression. I removed the valve cover to make sure the rocker arms and valves were moving correctly, and the piston was going up and down like it should. I tried blowing compressed air in the spark plug hole to see if I could hear where the air was going. All that did was to drive the piston down with great force. The dealer with a lot of experience looked it, felt the valve rocker arms while turning over the engine, and said he could not see any reason for the loss of compresson. He said it was possible that the one of the valves may be chipped, causing the loss of compression. That would be expensive to fix. I took the machine home and decided to check the valve clearance again, even though it felt the same. I found the exhaust valve clearance increased from where it was using the same STIHL gauge I used to check it before I had the problem. I then sprayed some SEA-Foam in the spark plug hole and let it soak for about 30 minutes. I still had no compression. I then tapped on the top of the exhaust rocker with a small hammer while blowing compressed air into the spark blug hole. This must have cleaned out a particle of carbon from the valve face, because the compression came back to normal. I then had to adjust the valve clearance because now it was too tight do to the valve closing all the way. I was amazed to find that the valve not closing by only a few thousands would show up as no compression. I have been using STIHL Ultra oil, and decoking the engine at the end of every year. What did I do wrong? The Decoke must have softened up some carbon that got trapped under the exhaust valve seat after running it for 20 minutes. Is it even necessary to Decoke when using the STIHL Ultra oil? Would it be better to use SEA Foam instead of the DeCoke fluid? It says on the SEA Foam can it can be used to remove carbon. The dealer said most commercial users don't even bother to decoke their engines. I really like the performance of my 600, and want to maintain it the best way I can. Thanks for any thoughts or comments you may have about this.