5200rpms at 70mph, too high!! kz1000m2

Speedos are easy to check with a GPS unit.  Secure one to the handlebars & ride.  Check at many velocities.  Most read higher at higher speeds on a sliding scale of sorts.  Nature of the beasts
If you can get hold of an old style dwell/tach, they can read RPM from the primary signal at the coil to check the accuracy of the bike's tach.

Good Ridin'
slmjim & Z1BEBE

slmjim+Z1BEBE wrote:

Speedos are easy to check with a GPS unit.  Secure one to the handlebars & ride.  Check at many velocities.  Most read higher at higher speeds on a sliding scale of sorts.  Nature of the beasts
If you can get hold of an old style dwell/tach, they can read RPM from the primary signal at the coil to check the accuracy of the bike's tach.

Good Ridin'
slmjim & Z1BEBE

Generally automotive manufacturers aim to be within 10% optimistic (never known one read under on speed)

Alright... so ummm... i was right about the spring being weak... it's broke when I was messing with it carefully. Im currently jb welding it so hope that's a good temporary solution. It'll have to wait for tomorrow... 

My speedometer reads 1-2% of what it should. At 80mph on GPS i clocked in 78mph. That's better than my car so im happy with that.

My Z1 speedo reads 25% high, I kinda got used to it.  60 is actual 45, 80 is actual 60, hasn't been a problem.  Someday I may get it fixed...

Every Kawasaki I have owned read 8-10% fast, so 1-2% is remarkable.

Alright, so I couldn't update you guys cause the power went out but I did manage to learn that the spring in the center really affects the reading of the needle. After repairing the spring,  the needle moved back to 0 way faster since the spring was essentially shortened. From reading 10.5k rpm before at max drill speed it now reads 8.5k rpm which is way too low. I broke the needle again,  repaired it,  and messed with it to make it "longer" and now it reads about 10.5k rpm again.
Basically what I learned is that by making the spring have more force bringing the needle back to 0, the lower your reading will be. So in theory if those people who have optimistic speedometers wind the spring counter-clockwise (I used the needle to do this) to stretch the spring more open to cause the needle to wind back more, their reading should be closer to home (or too far). However this is just my guess and someone else would have to verify what I'm saying by trying it. It's too bad that my spring broke cause there was a kink in it.

If your good with computer graphics, you could create a peel and stick decal to put on the speedo or tach face plate, with corrected number positions.