Motorcycle Repair: speedo and tacho, 1972 honda cb350, good shape

Question
1972 Honda CB350 K4
Speedometer – this works quite happily up to about 65mph albeit a bit bouncy, but then when I accelerate past this it goes backwards and settles about 40 -45mph. I can’t correlate this with the tachometer because this, reasonably steady at 60 mph/6k rpm, dances around the clock and bounces between 4k and 7k when the speedo has gone back to  40mph!
I have taken the cables out of the clocks and run a few drops of 3 in 1 oil down them but it didn’t seem to make any difference.

Answer
Hi Alan,

The cables can be a problem especially when
the needles bounce. You would have to replace
the cables to fix this.

The speedo drive unit inside the wheel
can also wear out so the wheel would
have to be removed to inspect the gear
drive and see if it is working.

As far as the tach and speedo themselves
there is no way to fix them other than
replacement.

I would check the cables for any stiffness
and then check the drive units next.
If these all look in good shape
and turn easily then it may require replacement of
the speedo and tach units themselves.

You might be able to soak the cables
in some solvent and then see if they turn
easily. You may have a bad speedo drive
in the wheel and maybe a bad tach cable
or tach unit or vice-versa.

The only way is to eliminate each part
one at a time to find the faulty part(s)

Good luck!
Wayne S.
------------