No this isn't a thread on how high you can rev your 914. Ha ha...


I'm wondering if anyone has a creative way of testing a tach on a bench?

I had noticed my tach was very "flippy" and seemed to go all over the place. So I want to run it on the bench and see if I can't cut some of that out.

The acuracy of the rpm input signal doesn't matter as long as it will deflect the needle.

Thanks!

-JR-

Any thought's anyone? Thanks!

Replace it with an Autometer tach

I built a 555 timer circuit with a mini rotary switch to select resistor values for 1000 - 7000 rpm in 1000 rpm steps (freqs based on 8 cylinder in my case). I have the 555 switch a transistor (open collector) connected to a relay coil (used for inductance). This makes a waveform that's pretty close to a real ignition system, but I'm thinking of using a real ignition coil instead.

real easy, and you own evrything to do it except a 2 dollar part

hook the tach up to a battery for the hot and the ground

take another wire to the ground through a small micro switch from radio shack on the NO contact. the micro switch looks like a 3/4 ich by 1/2 inch black piece of plastic with a metal lever sticking out. take another wire from common contact tot he connection on the tach for the coil

now the micro switch acts like the points you just need a way to open and close it very quikly, like a drill and a flapper sander or any thing the acts like a cam to turn the switch on and off when it rotates.

the faster the switch turns on and off the faster the tach shows

A jumping tac usually a loose wire or point and cond trouble. Try Petronics loose the points if you havnt already