docc,
have you lubricated the speedo cable? You can pull the inner portion out (while watching for little washers that may or may not be there) and put Lubriplate engine assy. lube into the cavity and reinstall the cable. You cannot get too much grease in here. This should help.
I wiped the cable down liberally with RedLine ShockProof. I do have some CRC engine assembly lube "with moly-graphite." You think maybe i should completely coat the cable with this?
And, will it work on my ZUMO?
Yes, put plenty on,in & at the cable.
As for the Zumo, if you find a cable there, lube it.........