Speedometer Reading Too Fast

[opcracer212]

I bought my 1982 Maxim last fall and, except for a short test drive before purchase, took first real ride a couple of weeks ago. I quickly realized the speedo seemed to be reading high. Check against gps confirmed it. Examples: 35 on the speedo is 30 on gps; 55 on speedo is 48 on gps.

The bike had an oversize tire on front when purchased, which I replaced with proper size. I thought the PO must have replaced the speedo gearbox to compensate for the larger diameter, so bought a replacement from another Maxim. But that didn't change anything.

Any ideas??

 

[Graham04]

Early Japanese speedometers were notoriously optimistic. Could it be a speedo off another Yamaha model. They often look the same.