Once you have set the saw as you layed out then you can tach it and have a reference point that you can return to.Never owned one but probably a good tool to have around.
With or without a tach ALL tuning is done based on results, not engine RPM's. I've been at this since the 1970's and have never owned a tach and no need for one. The best tuning method is to get the saw fully warmed up and set the "L" speed screw for best idle quality erring just a tad rich so it feeds adequate fuel to prevent stumble coming off idle, then move on to the "H" speed screw and start making cuts. There are plenty of threads and videos on the subject with details, etc.
As good as some of the videos are I'll add here that the "H" speed screw can be difficult with some saws especially if there are rev-limiting and/or timing retard features built into the coil as they mimic a correct "H" speed setting causing the saw to miss-fire or "four-stroke" at high RPM's. Doesn't really matter however because you should be setting the "H" speed screw a tad rich so the saw is both four-stroking and a tad down on power plus instantly four strokes in the cut when the load is removed, then cleans up nicely when the load is applied.
At this point I start going lean with the "H" speed screw paying close attention to four stroking at no-load/load removed and cleaning right up and pulling hard in the cut. This is when some coils throw you a curve ball so you have to know when to quit leaning it up and pay closer attention to how well it pulls in the cut. With non-limited coils it's easy because when you go too far the engine simply "runs-away" and RPM's go way beyond where they should and it does not four-stroke when the load is removed.
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With all saws tuned here I ALWAYS er just a tad rich vs lean. This lowers free rev RPM's just a tad, brings in more lubricant. lowers EGT's and for sure you will NOT smoke the P/C. To date I've never had a single P/C problem with any saw that I own or have owned and they are all flawless in the cut pulling really hard but instantly four-stroke if the load is removed, then quickly clean right back up when the load is applied. That is the key to success with these things and if you are using a tach it will be more for reference at that point and provide you with base settings if nothing else if you want to sneak a little more out of it or compare to posted literature or what others are finding with the same saw..........Cliff
PS: I saw generators mentioned here someplace. I tune them with a volt meter with load applied not with a tach. This is important because a portable generator will not have the ability to "clean" up the power like the voltage coming in from the power company. WAY back when I was on board ships and EOW in the engine room we had to "clean" up the power from ship service generators manually to insure the voltage supplied to all equipment was within specs, etc. Probably not a big deal if you are just running lights and such till the power comes back on but you could be a little hard on other items that prefer a more accurate power supply......FWIW....
Using a tach is the easiest way to have a saw that cuts bang on every time with minimal fooling around.
