Pertronix Tach Issue

[eastcoastz]

I know there have been a lot of topics on this but most of them are old so I thought I would start a new one to explain what’s going on and to see if there are any new ideas/solutions. 
 

I installed a Pertronix Ignitor II with a Flamethrower II (0.6 Ohm) coil. According to Pertronix, this is a matched pair. The car (1971 240z) has and continues to great with this setup. The issue I’m having is with the tach. 
 

When I first installed this Pertronix set, I had an issue with the tach not going above 3000 rpm. The car has no issue revving well above that, but the tach would stop at 3000 rpm and sometimes would even start going backwards. 
 

I talked with Pertronix tech support and they recommended that I put in a ballast resistor which I did and then the tach started working perfectly (for weeks). 
 

Fast forward to today, the tach started doing the same thing (stalling at 3000 rpm) even with the ballast resistor.  At random times it will go above 3000 rpm if I rev it up in 2nd gear for instance but even then the needle bounces around and then when I get to a cruising speed it stays stuck at 3000 rpm even if I push it in 4th.

 

I can’t imagine it’s related but the only recent change I made was I swapped out the original 40A alternator for the 60A alternator from the 280ZX. 
 

Any ideas why the tach keeps stalling at 3000 rpm? What could I do to make it reliable again?  The tach had no issues with the points installed. 
 

Thank you!

[Zed Head]

Near the end of the Crane XR700 / XR3000 instructions there is a section on modifying Smiths type tachs, which is what you have.  Looks like they're reducing the power/size of the magnetic field by removing a loop of the sensing wire.

Here's a link to the downloads area, might be worth reading.  Page 16.

Edited October 31, 2022 by Zed Head
Smith to Smiths

[bluez]

Well this is interesting, several months ago I installed the same on my 12/70 Z.

Last week, was the first time I revved motor and noticed tach would stop at about 4800-5000 rpm.  Previously, never had an issue. Was thinking about going back to points. 

[dutchzcarguy]

8 hours ago, bluez said:

Was thinking about going back to points. 

I'm driving now for 22 years on points with my 240z and last year i put in some new points after 25000+ km's..  Not because it ran bad.. just to be sure it's good..  The old ones were still nice..  if i hear all the trouble with pertronix i'll never buy that junk.. 

My 240z left me ones standing beside the road.. and that was because it had no fuel.. going up the hill !!  😂

[SteveJ]

51 minutes ago, dutchzcarguy said:

I'm driving now for 22 years on points with my 240z and last year i put in some new points after 25000+ km's..  Not because it ran bad.. just to be sure it's good..  The old ones were still nice..  if i hear all the trouble with pertronix i'll never buy that junk.. 

My 240z left me ones standing beside the road.. and that was because it had no fuel.. going up the hill !!  😂

And I have seen a 240Z that no matter how much the gap and dwell were adjusted, it ran like crap. After the Pertronix was installed, the owner said he couldn't remember the last time the car ran so well.

There are two sides to the coin.

Edited November 1, 2022 by SteveJ

[dutchzcarguy]

23 hours ago, SteveJ said:

There are two sides to the coin.

Ofcourse.. if the axle of the distributor is old crap... you get that..  After 50 years of neglect the timing is all over the place. Maintenance is important.

[eastcoastz]

I switched back to the 3 Ohm Flamethrower I coil that I had laying around (without the ballast resistor) and now the tach works better. 
 

I like that the .6 Ohm Flamethrower II is higher voltage so I might try a 2.4 Ohm ballast resistor with the .6 Ohm coil. 
 

I’ll keep you posted. 

[bluez]

Just swapped out the PEI and Petronix, with the old points and original coil.

No longer have issues revving the engine.  Additionally, the annoying stumbling at 3k rpm’s is gone.  Much better.
Did notice that idling seems a bit off, I think it idled better before, need to recheck timing and carbs next.

This was not what I expected..

[Zed Head]

30 minutes ago, bluez said:

Just swapped out the PEI and Petronix, with the old points and original coil.

No longer have issues revving the engine.  Additionally, the annoying stumbling at 3k rpm’s is gone.  Much better.
Did notice that idling seems a bit off, I think it idled better before, need to recheck timing and carbs next.

This was not what I expected..

 

Any chance you could start a new thread, of your own?   Eastcoast has a tachometer problem.  You're tossing a whole new thing in to the middle of his thread.

[bluez]

Will do.  
Had thought my issue was coil/tech related.

[Zed Head]

It might be.  But that's why separating things will help.  Thousands of people, across many brands beside Datsun, have converted their points to the Pertronix system with no problems.  Your problem wouldn't be a general points versus electronic issue.  DutchZ is just being philosophical.

[w3wilkes]

I have the 280ZX w/matchbox and have the same problem with the tach, mine seems to stall at about 3,400RPM but the engine runs great beyond there. Been that way for about 15 years so I pretty much just ignore it. I pretty much shift by sound anyway, more eye time on the road that way too.