Captain Obvious

Without a complete professional heat treat afterwards, there's no way I would put welding heat to an internal transmission gear like that. It's just a reverse idler, right? Only engaged when you shift into reverse? I'm no transmission guy, but unless it looks like one of the teeth is going to come off and get wedged between other teeth (and avalanche), I would just run it the way it is. Make sure your clutch is adjusted properly, come to a complete stop before shifting into reverse, and put the trans into any forward gear first right before you grab reverse. Do those and it won't get any worse.

The 1972 round tops (3-screw) used different float needle valves in the front an rear carbs. Does anyone have the length measurements for the original long and short 72 needle valves? Here's a pic for (what I believe are) the earlier 70-71 round tops. The length of the valve (just the valve without the sealing washer) is 18.5mm (0.729 in😞 After all that I've read, it is my belief that the two 72 valves should be on either side of the valve measured above. In other words, I'm thinking the front valve should be longer than 18.5mm and the rear should be shorter than 18.5mm. But without having the parts here, that's speculation. So anyone have some original 72 long and short ear valves handy they could measure. Or anyone have any old ones they replaced before that they would send me to poke around with?

Under certain circumstances, exhaust gas is intended to be ported into the intake stream to reduce some exhaust emissions (compounds of nitrogen). Now about those "certain circumstances"... Those certain circumstances never include "at idle". At idle, the EGR system is disabled because it tends to make the idle unstable. And when you're not at idle, amount of vacuum applied to the EGR valve is modulated by the BPT valve so that the higher the engine load, the more exhaust will be recirculated. I'm thinking that what you have done is applied 100% full open exhaust recirc under conditions where there should be zero. And the engine doesn't like that. Here's a bunch of EGR and BPT theory in this thread: https://www.classiczcars.com/forums/topic/47123-egr-system-theory-behing-bpt-valve/?

I don't remember the progression of events from the whole rebuild thread, but these flat tops are not assembled correctly. The front and rear bodies are swapped and will not work as assembled. I'm guessing this was just a proof of concept pic to show off the shiny new plating.

Love the pic with you next to the new Z. I think you look better than the new one. But that's just me.

Just to make sure you're numbering the pins on the 35 pin connector, here's a pic looking into the harness. You can use this to double check your results:

Datsun changed the power valve a number of times trying to get it right. I think the "green dot" version is one of the later versions. Here's a pic of one of my power valve springs. It looks like the one from your green paint mark version:

I wouldn't have expected that. That would have been quite the surprise!

Yes, mine has been filled in a lot on the left, and around the spark plug as well. That's not just a shave that made the spark plug area look like that. I was also thinking that the wall down towards the valves was too abrupt. But that could easily be sloped off a little more gradual by removing some of the infill. By it's next owner.

Maybe she's just happy seeing light at the end of the tunnel when you come back inside the house and aren't living out in the garage? Haha!

Here's a pic of one of the cylinders. Not as much material added as the one in your pic, but definitely a bunch added. Does this look reasonable? My days of building up a 300 bhp motor are behind me.

That's awesome!! So just how big was the smile??

Some notes about the temperature sensor and the thermotime switch. There are two trouble spots with the connectors. First trouble spot that the electrical connectors up at the thermostat housing are the same style and it is possible to get them mixed up. Other than the color, I'm not sure if there's a quick visual way to tell if they're correct. (If original stock) One of them is brown, and the other is gray. You can see the colors in the pic you posted, but I don't remember which is which. The second trouble spot is caused by the fact that they used two short pigtail harnesses to those two devices that end in bullet connections right near the #1 fuel injector. So since they're bullet connections, they could be swapped there too. One of those is supposed to be wrapped by a piece of tape (red I think) as an identifier, but many times, that has fallen off over the years. So I'm not saying yours are swapped, but the point is, that even if you have the connector on the right sensor, they could still be swapped elsewhere. You'll know for sure if you check the resistance tests in the FI bible. Last note is about the thermotime... The only time it should do anything at all is while the engine is cranking trying to start. It should be completely non-existent at all other times. So it should have no effect while you're driving around. If you want to, you can completely unplug it to see what happens. Might take a little longer to start your car when the engine is cold, but other than that, you should notice absolutely no effect.

Jon, What's something like that worth? I've got a P90 here collecting dust that someone has done that kind of work to. Not quite as extensive, but similar.

Have you done any of the testing from the EFI handbook (commonly called the EFI bible)? https://atlanticz.ca/zclub/techtips/efisystem/280zfuelinjectionbook.pdf Most of the testing there is done at the big ECU connector. I would be interested in hearing what your coolant temp sensor resistances are both cold and hot. And about pulling off a plug wire to check for a misfire... Not good for the ignition system. A better way is to pull off the injector connectors one at a time and see if the idle changes. Lastly, your compression numbers are definitely low. Did you block the throttle wide open while you cranked the engine for the compression test?

Pooky, I'm not sure I understand the problem(s) you're having... How bad is the problem? Is the car drivable? What's the worst of the problems? Maybe we can start there and knock them out one at a time? Also, @mgood is and active member and he's in the Pittsburgh area. Maybe he has some input for local help?

Well regardless if they flow the same, that's pretty annoying. The color may not matter, but on my engine, I would want everything to at least match. So I have no idea if the size of the opening on the bottom is the only thing that would affect the flow rate. I kinda doubt it. I suspect there are other internal geometry areas which could affect the flow rate too. In other words... Just because the hole in the bottom is the same, I wouldn't assume they flow the same. You could test them to compare the rates:

Sorry. One more thought about the timing chain and the tensioner sticking out... So the 240 slack side guide (the curved side) has a slotted hole at the top and two holes at the bottom. You have your guide with the bottom bolt going through the inboard of the two holes. I know this because I can see part of the outboard hole poking out from under the bolt head. But a pic here from @siteunseen, he has his lower bolt through the outboard hole. This effectively pushes the guide further in and tightens the chain: While putting in a whole new timing set is rarely a bad idea... What are the chances that the majority of the slack in your chain is due to an improperly installed slack side guide? I'm more of a 280 guy and the 280 guide is a little different. Just one hole that the bottom so no decision making on which hole to use.

Well color of the plastic doesn't necessarily indicate the flow rate of the injector, but to answer the intent of the question... Yes, if the new injectors flow more than the old ones, then you'll likely have to retune the system. But hopefully now that you have the other bugs and issues worked out, it should be a much easier process.

Good. I was thinking that some of the timing kits do not come with the guides, and I would certainly take the opportunity to replace the guides if you're doing everything else. Man that tensioner is really hanging out there. Looks like you were on the hairy edge of that thing popping out of there completely while the engine was running. Hope the new timing set takes care of all that.

Yeah, that definitely doesn't look right. Something wrong with the chain and tensioner, etc. Chain stretch, guide wear, gear wear... All together is allowing the tensioner to be waaaaay too far out. I think you need to pull the valve cover off and probably do a whole timing set. Easy at this point since you're in so far already.

Well lets see... If adjusted properly and working as designed, absolutely none of those items should have any effect at all at idle. Charcoal can - Disabled at idle EGR - Disabled at idle BCDD - Disabled at idle Cold star valve - Only active while cranking the engine, so disabled at idle

About the spring compression tool... You won't be able to use the "hooks on the cam" version if the cam is removed. (Duh.) Here's some pics of my latest valve spring took contraption. A little faster to use than my previous contraption since there's less wrench turning:

I spy something... Old Honda maybe?

LOL. I think he woke up not just thinking about one, but in fact, he work up WITH a Disney princess. I think you get significant bonus points for that!