I have an idea, that i want to try. I want to use standard cyclo-computer and place his sensor near magneto. The sensor is a magnetic sensitive element, which has 2 little steel "leaves" that contact when the magnet mounted on the bicycle's weel goes by. I'm curious if it's possible to set computer so it will show approximates value of engine turns. I have to calculate how to set "wheel size" to get good results.
I don't know if this device can record impulse so fast as magneto turns. If it could handle it it will be cheapest way to measure RPM's