Strange whirring sound - Tachometer

[eithr]

76 Suzuki GT380.

So, I had an eventful weekend working on the bike. Adjusted some stuff, fixed some things that I messed up from adjusting that stuff. Being a newb is frustrating. The one thing still not addressed... last week while riding on the interstate, I noticed the tachometer needle dancing wildly. In 5th gear, doing around 70-75 usually the needle sits steady between 5000-6000 rpms. I looked down to see the needle bouncing wildly between 4000-7000, despite maintaining a steady speed.

Once off the interstate, I could hear the bike better. There is a strange whirring sound coming from the tachometer. I'm guessing there's an issue with the cable and/or cable interface.

Any thoughts on what this might be?

Over this past weekend, I retensioned the drive chain, adjusted the clutch actuator and drained and refilled the gearbox. The tach sound was happening before these projects and was still happening this morning on my way to work.

[rbond]

The most common cause from your description, is it needs to be lubricated. Loosen both ends and if possible pull the inner wire out of the housing. Check it for signs of coming apart, if OK, use a grease gun and fill the housing until it oozes out the other end. Re-insert the inner wire and twist it as you go to coat all of it until it is fully back in place. Reconnect the ends, do not tighten them much or they (knurled knobs) will break! Take out for a test ride!

[johnakay]

[quote="rbond"]The most common cause from your description, is it needs to be lubricated. Loosen both ends and if possible pull the inner wire out of the housing. Check it for signs of coming apart, if OK, use a grease gun and fill the housing until it oozes out the other end

no no don't do that or you will definately bugger the tacho!
as the spindle( cable) spins this will force the grease up and if you put to much in it will find it way into the tacho.
now this is what you should do to lube the speedo/tacho cable,
draw the cable out wipe it clean ,you can also clean the outer case by washing it out using paraffin or turps nothing else,you wont damage the liner.
back to greasing smear and I mean smear the cable with grease,
put it back in and make sure every thing turns ok no scraping or tight spot.
if you find tight spot etc the outer casing could be caput.
keep the inner cable for spares and through the outer in bin.

[rbond]

I stand corrected by Mr. Johnakay. I agree with his method, I was too quick to give a proper (maybe) solution, so I did not think it through enough. Carryon!

[johnakay]

glad some one took note
I got this method off an old guy who had worked on bikes all his life.
he has since died.

[eithr]

Cool. Thanks for the advice. I'm gonna try to handle this situation tomorrow on 'work on the bikes' day. I'm supposed to help a friend with our first attempt to rebuild carbs.

[H2RICK]

Eithr, if the cable isn't your problem, then it'll be inside the clock itself.
Suzsmokeyallan can help you if the clock is knackered.