I have a tach, but I do not use it for tuning my engines. The only time I get it out is to compare peak RPMs for different props or when I'm adjusting the length of a tuned pipe. Here's what I do to ensure the engine is at a needle setting that will give it long life and few deadsticks.

While holding the plane with a firm two handed grip, have someone else run the engine up to full throttle. Then point the nose of the plane straight up. If the engine slows immediately, it's too lean. Lower the plane to the ground, richen it and try again.

If the engine speed doesn't change, it's still a bit too lean. Lower it, richen, and try again.

If the engine speeds up a bit and holds that speed, you've got it at a good spot.

If the engine speeds up significantly, it may be too rich. Lower it, lean it out a bit and try again.

This method has worked well for me for years. While it might be possible to squeeze a bit more performance out of an engine, the occasional deadsticks I get are not due to a lean engine.