Tach reads low with Duraspark Ignition

Two possibilities come to mind. First, on many Panteras with electronic ignition, the stock tach doesn't work AT ALL unless you use an isolater such as what MDS sells. Then, almost all work just fine. So I'd try to borrow a known-good tach & patch it into your car. No drive necessary- starting the engine should be enough. Note all Panteras and Mangusta tachs interchange.

Second possibility: the stock tach uses precision glass resistors (<1%) and I once found a cracked one inside on a tach's printed circuit board. Desoldering and replacement is simple compared to getting the bezel off undamaged so it can be reused, and locating a suitable replacement resistor.

Note the exact resistor value but as a non-precision component will change the calibration so you could be worse off than you are now. And fixing that is way outside my expertise. If a magnifying glass or VOM shows a cracked glass resistor or your tach shows signs of amateur work inside ( a resistor may already have been changed and picked now to cause trouble), try Mouser.Com. in the U.S. for a correct replacement.

My recommendation is to speak to Jon Haas at Pantera-electronics. He did two Veglia tachs for me and has the equipment, the talent and knowledge to repair these tachs correctly.

He can also help you with the wiring changes necessary to install the Veglia tach with virtually any ignition system.

Chasing this any further is just a waste of time and effort. Contact Jon.

It's not going to help you much, but my Veglia Tach works perfectly with my Duraspark II (Non-California, Blue Module).

As your review the Duraspark Diagram - it doesn't show a Tach Connection, but a look on the Pantera Schematic (Late-L) shows it coming off the side of the ignition coil that connects to the distributor (points side).  The Tach is powered by +12V.  It looks like there is a ground there too.

I am sure my Duraspark configuration did not modify that portion of the wiring.

I attached a drawing of the Tach Circuit for you.

I am with the others, who seem to be leaning toward a bad Tach.

There is no mystery - if you can borrow one, just make three alligator clips to the tach connections...  Clip #1 to (switched) +12V on your bulkhead, and #2 to the (+) side of the coil, and #3 to ground - then start the car.   Compare it to your dash reading.  This would pretty much be a two minute check.

Or pull your tach, and send it to someone who has the capability and expertise to test it (I am not being facetious here - that's a good suggestion, and if my test shows the remote Tach works fine - then that's what you are going to end up doing anyway...) 

Good Luck

Rocky

NOTE:  THERE IS AN ATTACHMENT BELOW THIS...  YOU HAVE TO CLICK ON THE WORD "ATTACHMENT" TO SEE IT. 

FWIW, When my MSD box failed, I wired up a Duraspark I box per the following George Pence schematic. Tach reading is accurate as far as I can tell.

Thanks everybody for the help and advice. I check if the wiring is functional and the same as in the picture above. If that does not help, I will give Jon Haas a call. 

I will keep you posted, as soon as I have a solution.

I remembered I still owe you an answer.

Because I didn't like how the engine behaved, a friend and I pulled it out and found a very strange (to me) combination of parts and building technique. Because I bought the car from a forum user here and don't want any bad blood I leave it at that.

Because of COVID getting the parts for the reassembly took forever, so I wasn't able to look into the tach.

The good news is, the engine now behaves like it should in my opinion.

The bad news is, the tach issue stayed exactly the same. I tested everything and even hooked up a completely different ignition.

So,  you guys were right from the beginning the tach is bad. Sending out the tach to the States from Germany is not a real option, so if anybody knows somebody in Germany or close to it who can repair it, or has a working one he wants to sell, let me know. 

Thank you all again

Georg

I would recommend to you that you contact Jon Haas at Pantera-Electronics.com. He has quite a bit of experience with the Pantera tach.

Stop guessing and trying to read tea leaves. You aren't going to find a solution on the internet. It doesn't exist there.

The wiring on a Pantera is a little out of the norm of what you expect and can give you fits when you delve into different then stock ignition systems.

I am running the Motorcraft Duraspark II distributor along with the Pantera-Elecronics Ignition Adapter. EVERYTHING just plugs in and works as it should.

I tried running an MSD and as par for the course with MSD, was a complete disaster and more importantly a waste of time and money.

You can do it the cheap way and try to screw around with it yourself and still be confused or even MORE confused or you can go directly to an expert that can fix it. Go to Jon.

The Pantera-Electronics system is the only system that works. PERIOD.

"Living in America is really neat. You don't have to run through the jungle and scrape up your feet." - Randy Newman. Of course if you want to scrape up your feet...go right ahead!

Note on the diagram Chuck provided R2 is a calibration pot. Maybe it just needs adjusting. Mine did.

Forestg may be right, it sounds like your tach is just half speed. Fiat 850 has the same tach...well, as nearly as I can tell, and I can only guess that the tuning of the variable resistor makes a difference for 4 or 8 cylinder. But as long as you are connected to the coil, there is no need for a "tach amp" (taking the big inductive kick to detect a fire). You would need a tach amp if the drive were "digital" (of just 0-12v). If only I would have known that when I put the Electromotive ignition on my 308...

Some Speedo shops (Palo Alto?) have standard circuit boards that replace the Veglia printed circuit board and work from either the digital input or the coil based pickup (see pic). That Veglia circuit is simple, and about the only thing that can fail is a capacitor--which are just pennies to buy. See the components with cracks in them--capacitors age and fail.

One of the projects I have no reason to finish is taking a 8krpm stepper motor Tach (about $30) and installing it in the Veglia can... but if you have patience to gently remove the bezel ring, I would try to wiggle that variable resistor there at 12:00 in the second picture...Lee

"Never set a cannon to kill a mosquito" - Confucius

@panteradoug posted:

"Never set a cannon to kill a mosquito" - Confucius

...Unless you are the kind who really loves a good cannon... One of those "this is really stupid, there is no reason to do this" things...but hopefully finishing one project I didn't need to finish makes up, somehow, for the others I still need to.  I started with an 8k chinese stepper tach, cut off the leds/switches, trimmed the plastic Veglia frame (which provided a snug fit to the stepper motor...locate the mounting holes to the original dial, splice about 6 wires to replace the PCB I cut/drilled away, bore out the 0,6mm shaft of the indicator needle to fit the new shaft, and voila ! Something to go into the closet, probably Lee