Tach reading 1000-1500rpm to high??

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70dusterpink

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I have a 67 barracuda With a 318, 904, 4.10 gears...
Running a 25" tall tire...

At 60 mph I calculate my rpms to be 3300....

My tach is reading 4500-5000 cruising around 50-60mph...

The tach reads 3500rpm when I am going 41mph...

I know this is way off.... What could be the problem... It's a aftermarket tach... It's old... What side of the coil should it be hooked to? Maybe I have a bad ground?

As a side note i was wondering why the car wasn't coming alive till 4000 lol... Because that's more like 2700 lol
 
negative side of the coil. i recently had a new sunpro supertach II do the same exact thing to me. it went in the dumpster
 
Well, a friend of mine was just saying his hi dolla autometer tach was doing the same thing,his turned out to be that the needle had spun on the shaft,probably wierd,I thought,but it did sound like your condition,his had been (shift point) set too high and was bouncing off the stop,when the ignition was turned on,like I said,fancy race tach in a street car.
 
I assume it's been this way since you installed it. Being older and possibly a more inexpensive one, make sure there's not a little dip switch on the back that has to be set to the proper number of cylinders.......4,6,8.
 
Most tachs I've ever used have a switch inside for 4,6,8 cylinder engines.thought I'd mention it since no one else did. If you didn't already I'd check to make sure it has one and is set correctly.

Too slow typing on my iPhone looks like oldmanrick beat me to it!
 
Dad n I just dropped our old factory tachs and 150 speedo off to have updated boards in them and calibrated. The guy at the shop mentioned he found trouble with Dashworx/RT Eng "updated" boards, that they would do the same thing at higher rpms. The guys we dropped ours off at said they will be "bang-on" The company we are using is Mr Heaterbox, here is their link
http://www.mrheaterbox.com/
 
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