Whacky Speedo

[Lbyvik]

I have a 1987 K100 RS.  Just hit 80K miles.  Did 8000+ this summer in 5 weeks.!  SWEEET..  VA to FL to Encinitas CA and back.  TOTALLY awesome and trouble free.  She NEVER hiccuped in the least

So anyway....Today i changed the rear tire. Put on a metzler something or other. All I did was remove the wheel, have the tire installed and balanced and put it back on wrenched lugs to torque specs.  I didn't touch ANYTHING else!  I swear!

So now I gotta break it in right???  Went and did about 180 miles of skyline drive and surrounding areas.  Twice while moving, the speedo needle did a wiggle waggle,  dropped to zero and popped back to the correct cruising speed. ( have had my GPS running so I knew what the speed should be)

Happened about 60ish miles in and again at about 90 miles.  It behaved properly the rest of way home. 

The only real variable is that I used a 130/80 rather than a 130/90.  But that only affects actual speed registered as the circumference is a bit smaller. (thats the reason for the GPS)  And before you berate me for using a smaller than spec tire, it works fine and it was brand new and given to me!

So the question is, WTF just happened and why?  did I knock the speedo cable loose when I mucked with the wheel?  what should I check?  I don't do my daily riding with the gps so I'd sorta like the speedo to be reliable.

Any ideas out there?

BTW  it was STUNNING on the parkway today!!

[Rick G]

To check if the speedo works or not and to troubleshoot you can remove the sensor from the rear drive and hold a mains powered soldering iron close to the sensor and it should read about 37mph with 60Hz mains and the key on. You can wriggle the connectors and see where the problem is but if the sensor is fried that wont work.  Measure the resistance of the sensor from memory about 220 ohms is the figure but continuity is the main thing.  There is a plug under the right side cover which can give trouble.

[frankenduck]

Not all soldering irons generate enough of an electrical field to fake out the K speedo sensor.

Flaky speedos can be caused by:

Sensor on the fritz and needs to be replaced.

Bad connnection at the connector near the rear master resevoir.

Bad connection at instr. cluster connector.

Bad speedo pin connection inside the cluster: http://www.motobrick.com/index.php/topic,449.0.html

[WayneDW]

Make sure the new tire isn't rubbing against the wire from the sensor.  That's what happened to me.

[TimTyler]

I witnessed my speedo freaking out while parked in the middle of a high altitude wind farm in Wyoming. I wasn't moving but the the needle was telling me crazy high mph. I got scared and drove away asap.