Wiring an aftermarket tach

I searched but, didn't find anything on putting an aftermarket tach on my bike (kz550). I was just wondering since its a waste spark system wont a regular tach from auto zone or something read double the actual rpm since it fires twice per rpm? I was thinking something along these lines...



^sunpro mini tach (2.25" diameter)

Check here:http://www.egauges.com/ATM_Tips.asp?TipPage=green_wire.htm The information may help.

I would think it would have to be designed for the aplication you want to use it for, Most after market RPM gauges that are universal have a switch on the back for "4"6"8" cylinders. So it would only"fire" half as the "4" due to the coil firing twice for two cylinders or How many Biker Dudes does it take to screw in a spark plug? Depends how much beer you have.:laugh: :laugh: :laugh: :laugh:

nelson8708 wrote:

I searched but, didn't find anything on putting an aftermarket tach on my bike (kz550). I was just wondering since its a waste spark system wont a regular tach from auto zone or something read double the actual rpm since it fires twice per rpm? I was thinking something along these lines...

^sunpro mini tach (2.25" diameter)

In the old days when we raced covered wagons, aftermarket tachs had a selector on the back for setting number of cylinders and that could adjust it.

A four hole engine double firing puts out the same signals as a regular eight cylinder engine.

nelson8708 wrote:

I searched but, didn't find anything on putting an aftermarket tach on my bike (kz550). I was just wondering since its a waste spark system wont a regular tach from auto zone or something read double the actual rpm since it fires twice per rpm? I was thinking something along these lines...

^sunpro mini tach (2.25" diameter)

You are correct that the reading will be off by a factor of two (when set to the 4cyl setting). The Gauge will show the RPM as half of what the motor is actually doing. This is because you would only be connected to one coil and getting half the firings.

To correct for that, you need an adapter to get signals for both coils.

Here is what I use with my Sunpro Minitach.



Those are pretty heavy duty diodes. You can get away with lower amperage diodes, but they have to be high voltage. You want at least 600v diodes. The voltage rating will be PIV or PRV (peak inverse or reverse voltage).

(This adapter won't work with the DYNA S ignition system. That requires a slightly different adapter.)

The biggest problem with those tachs is that they are not made to handle a lot of vibration. They are made ot be mounted inside a car... very different from a motorcycle handle bar in terms of vibration.

They work for awhile, though. I took mine apart and hot-glued the internal parts and that helped. I've got near 10 years on my Sunpro now.