CBR 600 sprocket change, speedo out

1998 CBR600F , previous owner had one less cog on the front sprocket, I
had a chain and sprocket change back up to standard cog. Speedo is now
way out, out by some 15% more I think.

I've checked Heynes manual and googled in this groups archive but
couldn't find any info on how to. Any ideas please?

 

If the speedo is driven by gearbox/output shaft then speed reading per
1000rpm should now be lower. But it should also now be correct.

If the previous owner had fitted some sort of gizmo-box-thingy that could
compensate for a change in gearing, then swapping back to standard wouldn't
change the readings by 15%, by my crap maths... On the R6 a change down on
the front made the speedo over-read by 6.667% and changing back to standard
would appear to make it underread by approx 9.34%, when actually it would
now be correct[1] again..

Dave

[1] as correct as a standard speedo can be, anyhow

 

WavyDavy emerged from their own little world to say

As WavyDavy suggests the previous owner may have fitted a gizmo between the
output shaft sensor and the instrument binnacle.

IIRC the cable is weather proofed from the sensor until it disappears
inside the fairing or under the seat. Trace the cable and just you should
find a plug where the weather proofed cable joins the main bike loom. This
would be the obvious place to insert such a gizmo.