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Author Topic: jumping tach needle  (Read 2372 times)

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Offline johnyvilla

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jumping tach needle
« on: February 28, 2010, 07:15:39 PM »
My 750's tach needle has been jumping around badly under hard acceleration, (Especially near redline) despite the installation of a new tach cable. Someone once told me a 'clean and lube' of the tach gears inside, might remedy the problem. Once inside the unit, I could see that there were no gears to clean and lube; just the shaft that spins the magnet.

What can I do at this point, if anything, to combat this annoying issue? Is my tach toast?
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Offline Old Scrambler

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Re: jumping tach needle
« Reply #1 on: February 28, 2010, 07:55:54 PM »
I have solved this problem a few times by spaying some Dupont teflon or some graphite into the tach while holding it face up to keep the spray from running onto the face.
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Dennis in Wisconsin
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Offline BeSeeingYou

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Re: jumping tach needle
« Reply #2 on: February 28, 2010, 08:42:19 PM »
The tach on one of my XS650's was hanging up and slow to respond. I don't know how similar they are but here is what I did to fix it.  On the XS there is a bowl shaped part that surrounds the magnet and this is attached to the needle through a watch type spring and turns the needle.  This bowl is also surrounded by a shroud that is stationary but it fits very tight.  There was some type of lube that had collected between these two parts that had thickened with age I assume.  It caused a drag on the bowl. 
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Offline bird

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Re: jumping tach needle
« Reply #3 on: March 01, 2010, 02:03:51 AM »
My CB750 tacho and speedo did the same. Just age and things wearing out I guess. Short of getting new (expensive) ones, I took them to an instrument specialist who got them running fine. These guys are good but not cheap, so ask for a quote up front. And, how long it will take. They're a bit like piano repairers and the like. They know they're the only ones, so they take their sweet time. Good luck. ^^
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Offline johnyvilla

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Re: jumping tach needle
« Reply #4 on: March 01, 2010, 06:56:22 AM »
Hmm. The action feels smooth and there are no signs of extra lube. Any other ideas?
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Offline domer

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Re: jumping tach needle
« Reply #5 on: March 01, 2010, 09:07:28 AM »
bad bend in the tach cable? my speedo cable made a gnarly turn that caused it to bind up and jump around... till it broke.
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Offline BeSeeingYou

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Re: jumping tach needle
« Reply #6 on: March 01, 2010, 11:25:58 AM »
There is so little in there to go wrong.  1)The spring breaks. 2) The lube thickens 3) Cable problems.  One thing to check is where the square cable enters the tach.  Make sure this is a good fit and the fitting the cable enters is square and not rounded off a bit allowing it to slip.  Maybe something at the engine side of the cable?
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