You can check the R.P.M. of your Lawn-Boy using a cheap tachometer (19 - 25 dollars) intended for model airplanes, available at hobby shops or online from Tower Hobbies. This type of tach replies on light passing through the blades, so you have to remove your cover plate. I propped up the mower on a cinder block and held the tach with a spring type wood clamp for safety reasons.
Jeff
Jeff
