It is tricky to get some rpm limited saws right. Most people will tend to err on the side of caution. And that can make the saw seem like a turd. On the 7900, and the 6100, I use a tach to find the exact point where the coil begins to bust up the ignition. At that point the tach starts bouncing around. Then, I lean it out a little bit further. Once I have it like that, I take it to the wood, and see how it behaves. It should clean right up under load, and four stroke as the pressure is being lifted. It helps to have the tach mounted while you are cutting so you can verify that you are hearing a four stroke and not the coil cutting out the ignition. The 7910 with the lower rpm limit is even trickier.