Zed Head

You didn't show higher RPM like 3-4000. But it looks like a physical problem might be a possibility. Sticky needle maybe, something dragging on it. Worth taking a close look at the needle movement itself. Dust, crud, rust.

So the tach needle just sits at zero, completely still, not even a quiver until engine RPM gets to about 1500, then it jumps up and sits steady at ~1500 and works normally/smoothly up to the high end? Pretty sure that a 260Z already has the 2200 ohm resistor. It looks different than the later models but it's there. Since you have the tach out you could measure resistance back to the coil negative. You could make three or four jumper extensions and run them out from the tach plug to wherever you want to set the tach for testing. Still have to start the engine but not so tedious to run a test.

I think that there's a drawing at the front of the Engine Fuel chapter of the 280Z FSM. An exploded view of all of the EFI components.

1981 280ZX Turbo. Looks good. 13,000 miles shown. https://bringatrailer.com/listing/1981-datsun-280zx-turbo-6/

I scrolled down the comments and at least three different guys have bid over one million dollars. But people are still picking over the incorrect door handles.

@Dave WM knows about reverse problems, he has some parts, and has worked on trashed transmissions. They are surprisingly durable. Reverse is a simple mechanism and can be reached from the backside of the adapter plate. Shouldn't have to remove the front case although that would let you inspect the synchros and gears. If the drainplug is in it see if it has metal stuck on it. Most yards drain the fluids though before they put them out so it might have been wiped already.

Not sure but I think that I've read about tachometer schematics somewhere in the past. I found a couple of old threads but not sure they go in to that level of detail. If you have the right meter and the capacitor still works you could measure it. Or, rearranged words, if you have the right meter and you can measure it, it still works.

Thanks for following up on the switch. It's a good tool for somebody who might have one of the aftermarket FPR's set to 38 or 40, or an AFM that runs just a bit rich, and just can't get that last bit of leanness they need to pass emissions or get a clean exhaust smell. Just short that circuit and leave it. Very useful for tuning. You kind of reported the results in the wrong thread though. Here's the post just to tie things together.

Good catch by Dave, but have you gone back and tried again? You suggested that you had already tried the proper shifting motion, above. Right and down. Just saying...

This one? I wouldn't call that teal.

First gear is 3.321 in the Z and 3.062 in the ZX. The ZX is usually paired with a 3.9 diff, the Z a 3.54.

I did the right click trick on an image and found this one in MI. Seems fishy. Identical cars in MI and CO? Hmmm.... It's a scammer/dealer. Actually, it looks like the CO guy has the MI dealer advertising it for him. "**Vehicle Location is at our clients home and Not In Cadillac, Michigan." So there's a commission baked in to the asking price. Odd combo, CO and MI. https://www.oldcaronline.com/dealers/Classic-Car-Deals-Cadillac-MI https://www.oldcaronline.com/1972-Datsun-240Z-Cadillac-Michigan-for-sale-ID956188.htm

Looks interesting but the keywords list says he's either a professional salesman and it's not really "his" Z, or he's a scammer.

This seems to fit these crazy times. Make America Mike's Again. https://www.mmafighting.com/2020/11/27/21723193/tyson-vs-jones-jr-weigh-in-results-mike-tyson-outweighs-roy-jones-jr-by-over-10-pounds

Modified 72 with a recent tuneup! It's a Z sellathon. https://bringatrailer.com/listing/1972-datsun-240z-151/

$38,500 for a 108,000(?) mile refurbed 73.

This one is about to end if anyone wants entertainment.

The wiring is the same without the ballast resistor. If it ran for 6 months it was probably right. Check the play on the distributor shaft. That will affect the air gap. The screw is just as tight as you can get it with a hand screw driver. Sounds like yours just came loose. You're saying that you reset the gap and it runs now right? You're probably good to go.

That's the Remover. AK260's was the Converter. https://jenolite.com/about-us/faq/

If the engine's not running sometimes reverse will find a spot where the teeth hit and don't mesh. If you can find a way to turn the propeller shaft it might go in to reverse. Worn out shifter bushings can cause shifting problems also.

Check the inside of the distributor. The triggering mechanism can wear, there's an air gap to set. The magnetic pickup coils go bad also, there's a resistance measurement to take.

How about a blender and a bucket of lemons? AK260'z Jenolite uses lactic acid. https://www.classiczcars.com/forums/topic/64766-citric-acid-and-rust/?do=findComment&comment=611145 https://jenolite.com/pdf/rust-converter-msds.pdf

I've wondered what happens to the valve angles. Their center lines moved with the warpage but aren't corrected by the shaving. So the tips of the valves will not be parallel with the rocker arm tips. The arms can twist as they move so it probably works out. If they skimmed the valve heads that will make them parallel but they'll have a slight side to side movement as they move up and down. Just one of those odd things to consider. So you're going to remove combustion chamber material from the small volume chambers to match them up? Make them all 54.8 CC?

That actually looks very clean. Not really worth doing more to. If you start using a detergent oil most of that will clean up as the engine runs. The brown color isn't from overheating it's probably just from blowby, combustion byproducts that have deposited up there. Not hurting anything. The brown color on the cam lobes is because the anti-rattle springs keep the rocker arms off of the cam base circle if the lash is set correctly. There's no rubbing there, which is good. It's also a good sign that you don't have any sunken valves since that will reduce the lash. Can't remember the year of your car (you should create a signature on your profile with information), but sunk valves were a problem before about 1976. Check the notch and groove on the timing chain sprocket to get an idea of timing chain wear. Make sure the tight side of the chain is tight and the timing mark is on zero.

Be nice though. The mechanic would have tested it while it was cold. So he/she would not have known, it would have worked perfectly like you said. Make sure it's nice and hot so they get full effect.