Hi guys,
I bought a tach last summer to check RPMs of my engines. Some guys say you need one and others will say you don't. I can only tell you I don't think they're worth the price. I tune my engines by sound and never burned up one. I start out with the engines running rich and slowly lean them out until they have a nice smooth sound, then I leave it there. If while flying I hear the engine running rich, I'll just lean it out a couple of clicks and again, leave it there. I may need the tach when I start flying my B 25 with 4 strokes to syn the engines.
Larry