Tacho help needed!! Ratio issue

[n0regret5]

Hi guys, I need to figure out how to find the ratio on my tacho, as I wanna replace it with something much smaller, and so far I've found two potential replacements, one is 1:2 ratio and the other is 2:1. The bike is a GN250.
I don't want to replace it with a digital one, as the cost is prohibitive ($150-$400) and I want it to stay analogue for the classic aspect. Anyone know how?

 

[n0regret5]

29 views and no help? Thought someone on here would be well-versed in this kinda stuff...

 

[teddpage]

If you wanna figure it out, you will have to find the tach output (where the cable attaches) and count how many times it turns when turning the motor one full revolution. That will tell you the ratio of the tach.

I had a similar issue when wiring up an aftermarket speedo.

 

[Speedshop]

Japanese tachos are usually 4:1