Koso Tack malfunction

[vamootsman]

For some reason my tach works fine until I roll off the throttle. If it says 6000 rpms it will make a quick jump to 12000. I never know what my rpms actually max out at because of it. Any ideas why and possible fixes? To be clear, it does it at whatever rpm its at, not just 6k. If its at 7k it jumps to 14k etc. except that it never reads higher than 15k. I think 15k is the max the tach will read.

[MikeP]

My koso tach has always done the same thing. Thought it was normal. Otherwise works just fine.

[vamootsman]

Anybody have any idea why this might me happening?