I would bet good money its not grounded well. Check your battery connections and grounds. Save tach money for cold beer.

 

Not saying this is your problem, but 11 volts at idle? That don't sound right...

On the conventional round individual tachs (and round speedo) contrary to popular belief, they can be disassembled and reassembled. It takes time and patience (about an hour to disassemble).

Basically you start with wrapping some electrical tape around the body of the speedo because you will be prying with metal screwdrivers and it will scuff the finish if you don't use the tape.

Using a small regular head screwdriver start slowly prying (lifting or raising) in very small increments at the stainless steel ring (lip) from the backside of the ring/gauge. Only lifting a little at a time working your way around the entire ring. Once around, start over with a little larger screwdriver all the way around, again lifting the lip a little more, then again repeat with the next larger size screw driver.

Do this as many times as needed to get the lip raised enough to finally pull the ring off. Always be careful with the screwdriver, you don't want to push the screwdriver in so deep that you will dimple ring from the screwdriver hitting the inside of the ring while prying. Again DON'T PRY TO MUCH AT ONE TIME OR YOU WILL TEAR THE STAINLESS STEEL RING. That is why it takes so long to get it off. Raise the lip in small steps to prevent tearing and again don't reach in too deep with the screwdriver or you will make a little raised dimple on your stainless ring.

I have taken 4 or 5 apart now, most of them to clean the damn water spots on the inside of the lens, one from a screw that came undone, and another to get a dead spider.

Putting it back together is the easy part especially if you have a drill press, but all you are doing in folding the metal back to it's original position. I used my drill press with a clean rag on the platter of the press to avoid scuffing the trim ring. Put the gauge face down on the rag/platter and use a 1/4 or 5/16 in drill bit installed backward in the chuck and use it as a press to press the raised metal lip back down. Keeping some pressure on the entire back of the gauge to squeeze it together while pressing the lip down with the press makes things seal up well and tight.

If doing it by hand, again, lay it face down on a rag on the bench and use a flat faced rod or even wooden dowel to start pressing the raised lip back down. I usuall do 12:00, 6:00, 3:00, the 9:00 oclock. Once I have the lip on those four areas pressed back down, I don't need to hold pressure keeping the gauge pressed together. I can now take my time working around the gauge pushing the lip back down till done.

Believe it or not, that is the short version of how to do it, but it can be done. Hope this can save a few of the gauges that are out there, and this is instructions for the analog odometer gauges, not the digital ones. Never done one of those...BTW, I think there are a couple vids or "how to" posted on youtube/google. YD

 

ya this is my gauge cluster http://pinwallcycle.com/images/vehic...91-05-0027.jpg

 

My tach on my 97 fat boy jumps a lot at low speed/rpm but seems to smooth out once I get going and the rpm's get up there.

 

ya mine is doing the same gotta be internals of the tach or a ground, but I'm betting the tach

 

I know its an old thread did anyone resolve their issue, Mine jumps from 0- 1000k at idle then will smooth out as i drive only at idle it bounces kinda like keeping up with the engine vibration...