Tachometer Problem

[Red Diamond]

Purchased a Tach from a 98 Standard, mounted it on my rescue 03 Standard. The tach seems to work well when the engine is revved up, but at idle it drops down to almost zero. What could be the problem? It came with the original wiring and I just plugged it in. The wiring schematic indicates that the wiring to the tach comes from the ICM, after that I'm at a loss. Any help would be appreciated. TIA.

[rhinor61]

why did you replace your old tach?

[HayHauler]

It sounds like his rescue bike didn't come with one, so he bought one and it isn't working at low RPM. 

But, I don't know why it isn't working.

Hay 
Jimmyt

[Red Diamond]

Thanks Jimmy, you're right, didn't have one. I will check all my connections after I finish with this beautiful day of riding. This will be my first ride of the year.

[R J]

What RPM do you think it is running at on the idle?

When I used to set mine down to 500 just to piss off my Harley buddies, it would almost drop to zero, but as soon as I put it back up to about 900, it worked correctly.

Sounds to me like you might be a little low on idle RPM's.    You realize, this is a Wild Assed Guess.

[Red Diamond]

What RPM do you think it is running at on the idle?

When I used to set mine down to 500 just to piss off my Harley buddies, it would almost drop to zero, but as soon as I put it back up to about 900, it worked correctly.

Sounds to me like you might be a little low on idle RPM's.    You realize, this is a Wild Assed Guess.

Thanks RJ, sometimes a WAG gets you to the heart of the problem. Certainly better than the guess I had.

[Joevalk]

Tach fluid has air in it, bleed the air off

[Red Diamond]

Yea Joe, I cranked down on the little needle valve that controls the fluid to the tach to keep it from fluttering. It still didn't work any better, guess the fluid is ok.