I bought a Stihl FS90R string trimmer a few weeks ago. It was my understanding that the valves should be adjusted at about 50 hours of operation. I think my trimmer has had at least that number of hours. When I left the dealer with the new piece, I looked at the service tech standing there who had fueled it, and got it running. I said, "check valves at 50 hours?" and he said "yes." I asked, "... instructions in the manual?" I was holding the bag with the Operators Manual in my other hand. He replied "yes." Now that the time has arrived, I look in the manual, and find nothing about "how to." I see it on the chart of things "to do." I did a search in this Section and found some threads discussing the topic. The responses ranged from "never have done it," to "it is absolutely necessary." And there were some others that said "it was important on the early models, but not so on the later ones." Some of these posts were a couple of years old. Nothing on the topic was very current. Also, I think the manual says 0.002" clearance on both intake and exhaust. But, I see some other values in threads posted here, 0.006, 0.008, and 0.010. My question for the new buyer in 2008: Is it important to do? If so, are there good instructions someplace? I see somebody mention a kit of tools, that includes a feeler gauge. If I buy a kit, will the kit have instructions? I have feeler gauges, but one of the posts said a very narrow one is needed for the job -- either get the kit, or modify an existing one with cutting. Now that the 4Mix engines have had much more use, maybe some of the comments in the older threads of a couple of years are not appropriate any longer because of engine changes. I'm just asking .... Thanks.