Here is what you search on Ebay they run about 35 to 45 dollars and work real good.
Electronic Specialties Digital Clamp On Tachometer

Electronic Specialties Digital Clamp On Tachometer

Model 325

Description:

No wires, no cables, or fragile antennas!

Conventional and DIS ignition system capability
Measures up to 12,000 RPM on conventional ignitions
and up to 6,000 RPM on DIS ignition systems
Data Hold and Low Battery Indication
Just clamp over any spark plug wire!
EZ-Tach gives accurate RPM readings quick and easy

TEST RANGES:
RPM4 (conventional) 0-2000 & 0-12,000 (x10RPM)
RPM/DIS (DIS ignition) 0-3200 & 0-6,000 (x10RPM)

EBAY LISTING

Pops is this it ?

:old: That is it I have had one for a long time most four wheelers and a lot of other motors do not have a tach. YOu can not ride with it but for working on it good thing.