I'm hoping someone can help me out as I want to get a aftermarket tacho but need to find out what ratio gear drive I have. It's a 1981 gsx250 and my options are 1:4, 1:5 or 1:7
Clean the end of the tacho cable and wrap a piece of masking tape around it leaving a piece sticking out like a little flag. Take off necessary cover to get to nut on end of crankshaft and fit a socket on a fixed bar, then rotate the crank 10 times and count the turns of your tacho cable flag. This will give you a ratio, ie 10 crank turns to 2 cable turns = 5 : 1.
Hi Bryce. Tach ratio is 1:4. I tested the mechanical aftermarket one I bought against the electronic tach the guy before me had wired in, and RPM were identical.
