After putting about 150 hours on my BR600 backpack blower, I decided to do the recommended maintenance, even though it was running OK. I first adjusted the valve lash. I could not determine what the original setting was, because I only had the special feeler gage for setting it. My standard gages would not fit the channel in the rocker arm. I found the gap was too large, so I had to decrease the lash. I wasn't going to de-coke the engine because I had been using the STIHL Ultra Synthetic oil. However, I felt I had a little more carbon buildup on the spark plug than I would like to see. I had been using 3 oz of oil instead of 2.6 per gal for the recommended 50:1 mix. Because of this, I also did the de-coke. When I finished, the engine ran even better than it did before. I mentioned this to my dealer, and he said they noticed the same thing after adjusting the valves. He said the valve lash was critical to the timing in that engine. I just wanted to pass on my experience with the STIHL recommended maintenance procedure on their 4-Mix engine. The BR600 is easy to start and really runs great. Charles Ranheim