What would cause my tach needle to bounce?

Mailman

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On my XS2, I had the tach apart when I refurbished the gauges. Everything was cleaned, everything is very solid feeling, cable is new and oiled, fittings are tight. The tach used to operate smoothly, then recently started bouncing in the upper RPM range. Now it bounces anywhere above idle. And I mean pretty big swings, for example if I was turning at 3500 rpm, the gauge would bounce from 3000 to 4000 RPM.

I’m not really anxious to open up that gauge again, but I’m trying to figure out the most likely suspect.

I have done a forum search and it usually came down to something was loose, but I’m not seeing anything that jumps out at me. Any ideas?
 

Jim

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Two ideas Bob.... if the inner cable is kinked, it's possible for it to catch momentarily... then whip around till it catches again. That'll cause a bounce.

Another is vibration. Rev the engine 'till it's bouncing, then wrap your hand around it to try and dampen out the vibes. If that reduces the bounce, then you'll have to figure out how to dampen it out.
 

59Tebo

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Another maybe, Bob, is the tach cable well lubed? You said so, but if the lube ran down into the motor, the cable might have gone dry. And a dry cable will cause a "bouncing" reading... :shrug:
 

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Right after I posted this, I was reading the thread “ speedometer stuck”. And it occurred to me that I have not tried spinning it with a drill. So I unscrewed the cable at the engine case and hooked up my drill to the cable , to run in reverse. And......the tach works perfectly! Smooth as butter, right up to redline. When I screwed my cable back into the case, I realize I can wiggle the cable , even when fully tightened.

Hmmmm......not sure what that tells me.
 

Jim

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Right after I posted this, I was reading the thread “ speedometer stuck”. And it occurred to me that I have not tried spinning it with a drill. So I unscrewed the cable at the engine case and hooked up my drill to the cable , to run in reverse. And......the tach works perfectly! Smooth as butter, right up to redline. When I screwed my cable back into the case, I realize I can wiggle the cable , even when fully tightened.

Hmmmm......not sure what that tells me.
Pretty much tells you the cable and indicator are good.... and mine wiggles when tight, so I suspect that's normal. A real longshot is slop in the gears in the engine... but that's a real stretch. I'm still thinkin' vibes.
 

Mailman

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Pretty much tells you the cable and indicator are good.... and mine wiggles when tight, so I suspect that's normal. A real longshot is slop in the gears in the engine... but that's a real stretch. I'm still thinkin' vibes.

Hmmm.....might just have to chalk it up to vintage charm?
 

Jim

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You try reving it and dampening it out with your hand? If that works, there might be ways to permanently dampen it. Are the mount rubbers new... or old and hard?
 

Mailman

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Are the mount rubbers new... or old and hard?

Brand new. I’m pretty much the only thing on that bike that’s old and crusty. :D

You try reving it and dampening it out with your hand? If that works, there might be ways to permanently dampen

I’ll give that a try next time I have it out. It might help.
 

Mailman

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You know I’m thinking about this, and I think my trouble might have begun after taking the cable off of the bike, when we got all interested in measuring cables. Maybe the cable is not being fully inserted somehow into the tach drive.
 

xjwmx

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When you ran it with the drill, I bet the engine wasn't running. New damping of the kind it came with from the factory made all the difference in mine. Good rubber grommets around the mounting bolts. New OEM foam ring between the bezel and the bucket made a huge difference. Might also try grease on cable instead of oil. Try to keep lube off of upper squared part that fits into plastic.
 

59Tebo

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I was planning on using "mini" gauges on "The Basketcase". In the Republik of New York State, a speedometer is an Inspection item. Are the "minis" accurate? Who knows. Tach? When the engine screams, shift. :yikes: Speedometer? If you're keeping pace with traffic, you're going too slow. :wtf:
 

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We used to see that a lot with speedometers in cars way back when. Most common cause was either a dry cable, used a light grease that was made specifically for that. Other common cause was a cable with a tight bend or opposing bends in a small area of the cable.
 

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59Tebo I have one and have double checked a few times if it was and it is. I ran a 107kms last Sunday and double checked the route via Google maps and was within a km. Speed with traffic guess it sorta is but seems it feels slower on my XS at speeds than with my Roadstar. :shrug:
 
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