Zed Head

Why not? Ask for a drive.

Forgot to ask also, does it have flat tops or dished pistons? It "should" have dished if it's a US market 280Z engine. Take a picture of the top of the block if you can. If it's built for racing you might not be able to get much out of it on pump gas. Might want to have it reset for street driving.

So it sounds like the mechanic was was right or partially right. If you look even more closely at the head it looks like it's been shaved, the combustion chambers aren't round. It might not be a typical "L28" head. Maybe an E88,which was a popular head for modifying, with a cam swap to a later self-oiling cam. The cam towers might already be blocked off if it's been running after it was rebuilt. Look at the bottom edge of the head right about where I circled in the picture below and you should see a letter and two numbers cast in to the head. E88 or N42 are most likely.

You ended up with 1/2 instead of 2/1.

This is your next #1 thing to do. The whole EFI system is based on a certain fuel pressure.

Or it might just have had a cam swapped in. My 78 head number is 247788. Yours is earlier. Could be a 75 or 76 US market head head which still had the spot for the pump, but used the spray bar (oil tube). Or a 77 head, which was the transition year.

I wonder if that's a non-US market L28. They kept carbs in the rest of the world for quite a few years after the US market went to EFI. You have the mechanical fuel pump mounts, for carb'ed engines, along with the self-oiling camshaft that came in about 1977 in the US market. Here's a picture of the boss for the pump, but unmachined, on a 1978 US market engine. A snip from your picture follows.

Should we start on the ZX's now? Here's 1979. Green is back!

Basically, all of the wiring diagrams are wrong. Here's what my 76 has. The fusible link blocks seem to be reversed, as noted. At least as far as wire colors. I haven't compared the circuits, either on the car or to the other diagram in the Body Electrical chapter.

There are a lot of pictures in this thread. Can't tell which picture you mean or evidence of what. Whose post are you responding to?

So Frankenstein found his car's fraternal twin. Dizygotic! (Found that when I Googled to be sure).

As EuroDat noted I can only count to two apparently. There are three white wires. I'll go out and count wires on my car soon just for fun and comparisons to the diagram. And, for reference and confirmation, I have a bona fide paper 1976 FSM and the black and white diagram matches the one in the back of the book, as far as this little snippet. It's weird that they don't have some sort of year ID on the legend. They do feel confident about the drawing though.

It's the connector wire between the fusible link and the battery. Shown in the diagram. There's a black one too, but it connects directly to the harness. Both harness connection wires are red (edit - screwed up statement about connectors here). If the ends get damaged you can't tell which is which.

1976 doesn't even have the colors indicated. They did change the wire colors though. 1978 is all W-WR through the links. 76 has only two white wires indicated.

Also, your title probably shows your 260Z as a 1975 260Z. That always causes kerfuffle on the Z sites. https://www.hagerty.com/articles-videos/articles/2018/10/23/what-to-look-for-in-a-datsun-240z-260z-and-280z

No real thoughts, just like a good puzzle. This chart shows 11/74 as the last "production date" date for US market 260Z's. Interesting. Maybe the stamped number is added when the VIN is assigned. 11 is pretty close to 12. You might have the last produced US market 260Z! Your VIN is about 9,000 higher than the last VIN they show also (edit - I was looking at the wrong line. 1975 260Z's go up to 200000). No idea where the chart came from. https://jdm-car-parts.com/blogs/news/vin-verification-of-us-datsun-240z-260z-280z-280zx

So shiny... I want to touch it with my greasy fingers too.

Could get even more expensive if your cores are no good. Time vs. money vs. convenience. He says the MC and booster are "new" but then he requires cores. So they're probably rebuilt. Many of the Rockauto and other auto store reman parts available today are of low quality though. So, you kind of need to have a vision in mind of what you want the final product to be like. https://zcarsource.com/core-disclaimer/

Sounds like it's lean in that RPM range. There's probably an adjustment possible. Don't know how the Webers work. Should have put Weber in your title.

Nice. Didn't even have to remove it. I wonder if Mark meant braze when he said weld. They're similar. You can probably accidentally braze when you meant to weld also. Be interesting to see how it holds up. If you didn't pin the ends with drilled holes, as suggested, the crack might just continue to grow from the ends. But they'll be small cracks. https://www.machinedesign.com/fasteners/when-brazing-beats-welding https://www.lucasmilhaupt.com/EN/Brazing-Academy/Metal-Joining-Welding-vs.-Brazing-vs.-Soldering.htm

Check your glue blobs. If you have a meter, measuring resistance of the coolant temperature sensor is easy to do also. Working on the EFI system is really just taking measurements and comparing them to a check list. Measure-check-measure-check.... If you get a bad measurement, you find the cause and fix it. When all of the measurements are in-spec. if the problem still persists then you go to the weird stuff. Often-times people adjust things to out of spec. trying to fix other out of spec. things. Forgot the glue blobs picture. Post #29.

I wonder where Nissan was getting the red ones? They don't seem to have a part number on them. Anyway, good to be back to normal and verifiable. All links should have a Nissan part number stamped on them. The Atlanticz page still suggests that red is 069 mm^2 though, so beware. The zcarsource pictures show a 1.0 link, not 1.25. And orange 0.35. They might get theirs from Japan but not necessarily from Nissan. Plus they say that 1976 is the same as 77-78, which is not right (look at "Additional Information" on their page). I'm just reacting to all of the words and pictures that are out there about fusible links. Lots of variation and confusion. https://zcarsource.com/fusible-link-cover-set-280z-76-78-new

Nothing specific to SU's but my understanding of "run on" or dieseling as we used to call it is that it's caused by hot spots in the combustion chamber. Why it was called dieseling. So, he either has dirty combustion chambers or sharp edges that are staying hot. High cylinder pressure would be more susceptible to dieseling. The common way to avoid it was to rev the crap out of the engine just before shutting down to blow all of the carbon out and get some fresh cool fuel and air in there.

Aren't these 240Z brake parts hard to find? You guys are making it sound like it's a simple go to the store, swap the parts. Especially the Master-Vac. Might be worthwhile to disassemble it and seal any small tears in the diaphragm before they get big. You know that brake fluid has probably been in there, the paint's peeling from the bottom of the booster.

Congratulations. The brakes might just need bleeding. The switch, cleaning. Have fun. My spare tire comment still holds....