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How fast should tach end spin -- how does the tack work

  • Thread starter Thread starter Anonymous
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A

Anonymous

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I posted in the General Discussion regarding some success in getting my GS running. I mentioned there that I had a tach problem before I searched for a solution.

I've done a search since, and I still have a couple of questions.

How fast should the tach cable end spin? I've fired the bike up with the cable disconnected at the engine then the tach. The cable is spinning, but not nearly as fast as I would have assumed -- the nub sticking out of the engine is spinning at the same speed. I had guessed that to register 1000 rpm, the cable end and nub would spin rather rapidly -- maybe not 1000 rpm, but fast enough that it would still be a blur. It is not a blur -- I don't know that I could count the revolutions for a minute, but I believe I could keep up for a bit.

How does the tach itself work. I had assumed there were some gears inside the tach itself that did most of the work. I read a post that suggested even the mechanical tachs used magnets. (I'm guessing there are gears somewhere regardless.)

The bike is an '81 GS850. The cable is not broken. The connections have all been made as they should.

Prior to some work I did this morning I had the bike running. The tach registered 1000 at that time. It sounded like it was running a lot faster. When it was all over I convinced myself the bike was running at 1000 but sounded funny due to being in the garage and needing new exhaust.

Today the bike sounds a lot better. The idle sounds a lot more reasonable The tach is not registering anything.
 
This is just a guess, I am sure some other person on here knows for sure, But I always assumed it worked just like a speedometer, with magnets and stuff.
 
The tach cable is driven off the EX cam, so at 1000 rpm the cable will be turning at 500 rpm, the tach itself is magnet driven
 
I've solved it. Please refer to "How stupid can one man be" in general discussion for the solution.
 
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