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Very good! You might want to get hold of a strobe gun to make sure the static advance is set correctly with the new distributor if you havent done so already.

Have a look at the plugs after the engine dies. If they are bone dry its most probably a fuel issue, if they are a tad wet and smell of fuel you need to have a look at the ignition. The advance mechanism is especially important to look at, as the advance weights could be stuck, fixing the distributor to the initial ignition advance. With the stock ignition i recommend using NGK BPR6EIX. Those are more expensive than the standard ES plugs but have a finer tip which is much better to get a spark discharge with the (low power) standard ignition. The engine will start more easily when cold or warm and plug fouling is reduced.

I would suspect the driver stage to be defective, probably one of the transistors especially as you mention that this gets worse with heat. Resistors are usually quite dependable, but the capacitor used for timing might have a reduced capacity due to aging. As a quick test, if you remove the blue wire from the coil/resistor, does the tacho still goes to 1000 rpm with the ignition switched on.

Tlorber, could you describe how the tacho behaves (e.g. is the dancing at specific RPM areas or already after switching the ignition on, does the incorrect display happen over all the RPM range or only at specific spots?). The symptoms could either indicate a defective tacho driver circuit or an incoming signal with a voltage level which is too high. If your tacho is indeed defective, i am happy to do a repair and calibration for the cost of the spare parts (if the magnetic coil for driving the needle is still intact, then it should be no problem) but you would have to send it to germany.

Thanks for the info, will do!

I have installed a nice vintage compe wheel in my '72 240Z and noticed that the indicator stalk (left) now touches the steering wheel. Have there been different indicator stalks depending on the wheels? I guess that i can carefully bent the indicator stalk to create some distance to the steering wheel, but wonder how this was handled back then.

As part of my switch to a Megajolt ignition i build a small electronic circuit to convert the "four wire" current driven Datsun tacho in my '72 240Z into an electronic tacho, which can directly be connected to the tacho output of the Megajolt, MSD, Bosch, Crane or other electronic ignition. Quite surprisingly, the 38 year old tacho was very precise after a calibration, with the highest display error below 3%. You'll find a complete description including the wiring diagram, pcb files and images here: http://www.dinoplex.org/tachoconversion/ Best, Adrian

No dash cap, just a standard 240Z with the original dash and instruments.

Thanks, it worked out as planned. Had to use pliers for the second wing nut, the first one was no problem. i pulled the bulbs from behind while tacho was still installed, then gently pulled out the tacho and removed the four wire connector from the front. Chris, on the '72 240Z you can just pull out the tacho in one piece without having to remove the dash, lucky me

Great, thanks! I'll try to do this without removing the dash first, wish me luck.

I need to remove the four wire tacho for a conversion from inductive to +12v trigger as i am currently installing a megajolt ignition setup. What is the easiest way to remove the tacho from the dashboard, can i just remove the locking nuts on the back of the tacho from under the dashboard and then pull it out from the front?

This post is a bit too late to help but just for the record The EFI requires a single kickback impulse per spark from the inductive coil setup to trigger the fuel injection. The "kickback" impulse from the coil is the reinduction from the magnetic field, a peak with about 100-200 volts (depending on the coil ratio and setup). You can see this quite nicely with an scope connected to the primary side using a probe rated for 500 volts. For setups with electronic capacitive discharge ignitions (such as the MSD 6A) there are adapters which turn the +12V square wave tacho trigger impulse from the MSD or ignition box into a high voltage kickback impulse by means of a small transformer. I believe the correct MSD part is 8910. The primary coil impulse(s) from an MSD setup cannot be used as you have multiple sparks up to 3000 rpm which will not work with the EFI (which expects a single trigger impulse per spark).

Not sure, but it also could be the flasher unit itself (at least it looks like mine). Its mounted below the dash on the mounting hardware of the steering axle. The cable colors are white and green.

A thorough test is to drive the car until the tank is empty, as described above. Then remove the sender cable from the fuel sending unit (should be the yellow one), and connect it to one cable of a Multimeter in resistance (ohm) measuring mode. Connect the other cable of the multimeter to ground. Set the multimeter to a range of about 2K (2000 ohm). Now, while filling the tank at the gas station you should see the measured resistance changing accordingly. If you want to check the fuel gauge itself, buy a cheap 1-2K Ohm potentiometer at an electronics store. Connect one of the two outer pins to ground, and the middle one to the senders input on the fuel gauge. Now, if you turn the potentiometer, the needle should move according to the setting of the variable resistor. http://www.parts-express.com/pe/showdetl.cfm?partnumber=023-510&source=googleps

Spitting sound could be the carbs backfiring, open the air filter box and check if the sound gets louder. Carbs backfiring is usually wrong ignition timing/and or mixture too lean.

I wouldnt assume that the advance mechanism is the (only) problem, as soon as you high rev enough the advance is locked out at the maximum anyway. Your symptoms do point to timing irregularities due to worn axle bearings, so a distributor rebuild is recommended at this point. If timing is not advanced enough, the engine will run rough and the exhaust smells of gas. Take care with too much advance, detonation can damage your pistons, rings and head bearing.

No idea, i'm living in the old world Maybe someone from the east coast can give a recommendation? It's a good opportunity to also get the advance mechanism overhauled!

Ok, that looks like you need new bushings , 1/16" is a bit too much for a hall pickup, imho. You don't need a new one, why not get your dist overhauled (new bushing, advance mechanism check), that might fix your symptoms.

I would guess that the hall sensor and magnetic sleeve are more prone to timing problems due to a worn distributor shaft/bushings than a points setup. So there is a good chance there were already issues with the distributor which you did not notice while using points. Another quick check, if you remove the cap and try to move the finger/shaft sideways, does it move?. That would be worn bushings and a possible source of timing/advance issues. If you try to turn it clockwise/anti clockwise and it moves, the gear is most probably worn down.

Elliot, posting #100, congratulations 028 to .030 is perfect. If the sleeve has some play it might start to vibrate at higher speeds, leading to erraneous ignition impulses. So make sure its bomb proof (i have used a thin copper shim for my installation and then epoxy glue to fix it on the axle just to be sure). If the shaft is wobbling then that might have a similar effect. A workshop handling classic cars or doing distributor rebuilds should have a distributor tester. I guess that there must be several workshops in NJ, NY or Philadelphia, Google maps listed several classic car services around your area. Another quick test to check out if its an advance or shaft/axle problem. Have a friend rev the engine up to the the problem spot (5,5K), hold it there and manually advance/retard the distributor by turning it. If you can find a position where the engine runs well, it is most likely a timing problem. If you cannot get the engine running smoothly that way, i would assume its an Ignitor pickup/sleeve/shaft issue.

So this should prove that the tach is not the culprit, also the measured voltage looks good! Next to the Pertronix call i would now focus on the distributor and check if the advance mechanism really works for the full RPM range and that the axle is not so worn out that it induces glitches in the Pertronix hall pickup. Have you checked the Ignitor module and sleeve installation? A test run on a distributor tester would be the quickest way to go now, do you have a workshop in your area which could do this check for you?

See the attached image for wiring the test without tacho. With your current wiring, remove the b/w cable to the coils (+) terminal (at this point, there should be no cable attached to the (+) terminal), and connect the wire marked blue in the image, leading from the Green/White cable to the (+) terminal. You are now testing the ignition circuit without the tacho to check if the tacho in line creates problems at higher revs. Rev to 5.5K RPM (you need to do that by listening to the engine) and check if the engine hesitates. You might also want to repeat the test with the timing light and see if it still flickers at high RPMs.

The plugs on my '72 look the same (three are lean, three too rich), i need to balance the carbs too but that should be nothing to worry about. Still a good a idea to have the carbs checked if you suspect anything. You did bridge the tach and the stutter still happens at 5.5K rpms, correct? So we can assume that the voltage supply to the ignition is ok, i would now focus on the distributor. Make sure that the pertronix installation is ok (sleeve, see above) and ideally have the distributor checked on a distributor tester, there might be a problem with the advance mechanism and or a worn axle. When you rev your multimeter goes into panic mode :classic: For each ignition discharge your coil also induces a voltage on the primary side, so when revving you get around 200-400 volt at the primary terminals. With a transistorized ignition such as the Ignitor you need to measure the voltage at the input of the ignition (ground & red cable of the Ignitor).

If you smell fuel then you suffer incomplete combustion, e.g. the fuel is not completely burned due to a weak, too late or missing spark. I dont think that this is an issue of running too rich, the engine would not hesitate at higher RPMs with too much fuel. You did diagnose the issue with the timing light, there is no consistent spark available at higher RPMs. Have you checked out yet how your plugs look like? If the engine is running rich, they will be black but dry. If they are wet and smell of fuel, its the ignition not doing its job. Check out the installation of the Pertronix Ignitor module in the distributor, and make double sure the trigger sleeves alignment to the sensor is correct and that the trigger sleeve does not move or is loose or wobbly. As the tacho is wired in line with the +12 feed from the ignition key, it might also be a source of trouble. Try to remove the tacho wire (black/white stripe) to the coils (+) terminal, and directly connect a cable with +12 from the ignition key. (The green/white stripe cable leading to the resistor is wired to +12 from the ignition switch, so you could connect another wire to the green/white stripe cable and then the coils (+) terminal for this test). Now check if the problem persists. No tacho this time so you have to run by ear.

BTW, if you dont have a current clamp, start by removing a fuse and use a Multimeter to measure the current between the two terminals of the fuse. Do this for all fuses to get a first impression.