Can a tach intended for a car be used on a motorcycle?

[Anonymous]

The motorcycle is a 1979 GS1000L. The tach and speedo are both inoperative. The motorcycle versions that JCWhitney has are fairly expensive, but the car versions are considerably cheaper.

So, I thought why not try to save some money.....


A friend tells me that because the GS1000L has two coils it requires a different type of tach than a car uses for the readings displayed to be correct.

Does anyone know if he is correct????

Thanks,

Rick

[Anonymous]

tachs for cars (in my experience) run off electrical pulses from the disributor cap and rotor. I dont think you can convert that for use on the gs engine since the GS tach uses a cable run of the exhaust crank shaft.

[Anonymous]

The pulses for a car tach, if it's electronic, come from the points (or trigger) side of the coil. The problem with hooking one up to a GS is,
1) two coils
2) each coil fires two cylinders, which means,
3) Each cylinder fires twice per cycle.

1 is irrelevant, we only need one signal. 2 & 3 is where it gets complicated.
Most car tachs are universal, and have a switch on them for 4-6 or 8 cylinder cars (sorry, Geo Metros are right out, being 3 cyl's). If I am thinking of this right (for instance, setting the switch to 8 means the tach knows that every 8 pulses is one revolution). We divide our 4 cyl by 2, (because of 2 coils), then multiply by 2 again, (because it fires twice per rev), so we should be able to set it to 4 and be good to go.

Basically, don't think to much into it like I just did.
I've never hooked one up to mine, but don't really see why it wouldn't work.
Go ahead, you try it and let us all know.

[RacingJake]

You need a Tach thats runs on 2 cylinders. Hook it up to only one coil and you are good to go. Hook one wire to the Pos side of the coil, the next one to the Neg side of the coil and the ground wire to the coil mounting bolt.

Jake