Topic: New CB 650, speedo off

[Professor]

Hey, last month I bought a really nice '81 model CB 650, my 3rd bike but the first in about 23 years, so I'm just joining the forum. The bike runs great, but the speedo is hosed up, slow responding, sticking, the odo seems fine, showing 10k mi (now 11k). So I'm guessing that the problem is at the speedometer itself. (the needle is slightly touching the inside of the glass).

Can I dissemble it, lube, or what? Also, anybody know about how fast I'm moving in high gear at 6k RPM?

Thanks!

[rob]

I have a '81 CB 650 custom, nice bike.  Post some pictures of yours if you have a chance.

I am doubtful that its just the speedometer, my first guess would be the speedo cable.   My speedo shows very similar behavior.. eratic movement of the needle at times, slow response, etc, and it is problems with the cable.  The odometer, trip counter, and speedometer needle are all run off the same gear system driven from the cable. 

To test this, I would head out to a strech of road that I knew the exact length of, measured with GPS, or a car, etc.  Zero the trip counter and ride the length of road.  Compare the distance measured by both the odometer and trip counter to the exact distance.  Try this while varying your speed as well.  This will give you an idea if it is the speedo cable or an internal problem with the speedo needle/gearing itself. 

Still, I would lay blame on the speedocable itself before taking apart the speedometer housing.  Try taking the cable off, inspecting the ends and lubing it, and making sure that the cable is attached properly to the gear in the fork.

As for how fast your moving at 6k RPM is going to depend a lot on the specifics of your bikes engine compression, carbs, weight, fairing, gearing, tires etc.  My bike at 6k does something like 110-120 km/hr (68 - 74 mph)

Rob

[cb650]

I would say 75mph also assuming the gearing is stock.   
I have a speedo if you need one.  Cables are cheap new.



          Terry

[glendaler]

6k brings me up to about 120km/h. it's a 79, and i also had to replace the speedo cable, the wheel end was busted. wasn't to expensive, and nothing to install. good luck!

[cb650]

I geared one of my 650s to do 75 at 5k.  Was to much though.  Nice by myself cruising but that all.





                   Terry

[rob]

Terry,

What is involved for this type of re-gearing.  Replacing the front sprocket? rear sprocket? both?

Rob

[cb650]

Biggest front,smallest rear and oversized tire.    Thats why I like Dennis Kirks "catalogue".   it lists what sprockets fit along with what is stock.  They dont have it online though. Or atleast they didnt.
The rear was listed as fitting the mid 70 yami 750 twin I think. It was to much gear though.



           Terry

[glendaler]

yeah the dennis kirk books are good for some specs, especially comparing part numbers to see what's interchangable. when i ordered my new sprockets and chain i was going to go down a tooth in the back but he said it probably would make that much of a difference so i just stuck with the stock gearing, i didn't want to loose much bottom end, i like that more that the top. he also suggested a a 520 chain conversion, i originally just need rear sprocket but he said it would be cheaper to get the whole thing in 520 than the rear and chain in 530.