Captain Obvious

Fuel pressure should be 36 psi minus manifold vacuum (in psi). So for example, if manifold vacuum is 16 inches of Hg, then the fuel pressure should be (36 - 7.8) or about 28 psi. The conversion for inches of Hg to psi is about half. One inch of mercury is about a half psi.

The symptoms of breaking up worse under load do make me think of an ignition related issue. Your different colors on the plugs might be a tuning issue as well, but load dependent misfires would have me looking at ignition stuff first. Plug wires arcing to ground somewhere, or coil wire arcing over to someplace it should not be going. Have you put in new cap/rotor/wires?

Great stuff! Funny though, (in my immature 13 year old brain) this me chuckle :

Not sure it really matters, but I think the 55425-N4300 is the strap for the 280's with the R200 diff. if you've got a 240, then I believe you want the 55425-E4100. My measurements indicate that the two straps are different lengths.

Yeah, I'm not saying that's the problem, just tossing out ideas and possibilities. From the other stuff you mentioned, like differences between plug groups, it certainly sounds like it could be an issue elsewhere. Happy hunting, and hope you get it running the way you want it!

Looks great. So when are you going into production? It sounds like there are a couple other owners who want those. Aint that the truth!!

Exactly. The only way the port into the side neck of the canister gets down into the carbon part of the can is through the little hole you plugged with a screw. I suspect that many of the original purge valves built into the cans don't work correctly anymore and I think your use of a new aftermarket purge valve is a cool innovative way to get around that. You just missed the mark a little bit with your original implementation. Glad to help.

I think I did that already. That's what my first three posts were. My first post was pointing out that your modification does not work. My second post was telling you how to fix it and actually make it work. My third post was additional info for you to help you understand why what you have done does not work.

That video was done by someone who knows how the system works. I'm not asking if he knows what the purpose of the purge valve is. I'm asking YOU what the purpose of the purge valve is. What is the purpose and why would you ever want it to open?

Yeah, if it's as simple as it sounds, it's likely that your wiring change is not what's causing the problem. However... Note the word "directly" that I used earlier. The reason I said that is because there may still be a problem with the 72 distributor you threw in there which is causing a problem. Points not set correctly. Dwell issue. Spark scatter from bushing wobble. Leaky condenser killing spark at higher RPM... Lots of problems could be caused by the distributor but might not be caused by the wiring modification you made. Point is, I'm not yet giving your 72 distributor a thumbs up, but I don't think the problem is your wiring change. Does that make sense?

I was actually talking about either the stock purge valve, or the aftermarket one you put in. Doesn't matter. Why did Datsun put that valve there? What is it's function? Why would you want to have that valve open? Ever? Why didn't you just cap off all the lines at the engine and pull the carbon canister off your car? I'm trying to confirm that you know what the purpose of that purge valve is.

OK, then let's start simple.... Why would you want to have the purge valve open? What would be the reason to ever do that? Explain to me why having the purge valve open is a good thing.

Adding that extra valve the way you have done it does not "work like stock". It does nothing functional at all with respect to vapor mitigation, and in fact, could actually cause engine damage. The stock system does this... The fuel vapors that come off the tank and temporarily stores them in the carbon canister. Then under certain circumstances while the engine is running, those vapors are pulled back out of the carbon canister and disposed of by burning them in the engine. That's what the stock system does. The system, as you have modified it does this... The fuel vapors that come off the tank are stored in the carbon canister. Until the carbon in the can becomes fully saturated and cannot hold any more vapors. After that point, any vapors that are pushed into the tank are simply vented to atmosphere through the fiberglass filter on the underside of the can. Also under certain circumstances while the engine is running, the purge valve will be opened and an unknown and unpredictable amount of fresh air will be pulled into the engine leaning out the fuel mixture an unknown and unpredictable amount. That's what you have now.

Oh, and to answer your question "I guess my end question is, how can I tell if this Duralast sensor is NPT or BSPT?" The answer would be "Use a thread pitch gauge". The 1/8 NPT is 27 threads per inch, while the 1/8 BSPT is 28 TPI. The two of them should be easily distinguishable with a gauge because the thread pitch is different. But if you don't have a gauge, you should be able to hold the two threads against eachother (with the teeth meshed with eachother) and see the difference. If the thread pitches are the same, the teeth will mesh perfect. But if the pitch is different, they will not.

So just make sure I understand everything... You bought an adapter that has female 1/8 NPT threads on one end and male 1/8 BSPT threads on the other end. And the Duralast sensor you purchased threads nicely into the NPT female end of that adapter. Is all that correct? And also, so how does that new adapter fit into the block? Unless I missed something, you didn't mention that.

Actually that's not exactly the case either... If your cap seals to the can now, you have effectively capped off all the vacuum lines. However, if the cap does NOT seal to the can (which is what I suspect), you have now introduced a vacuum leak of unknown volume when you are at light cruise on the gas pedal. The size of the leak will be determined by how well the plastic cap seals to the canister. And I suspect that cap seal is not that good since you took out the diaphragm material (because it interfered with the screw head). You will get good idle performance because the purge valve is closed, but at partial pedal position, when the purge valve is opened, you may run way leaner than designed. Not a good situation. OK, I think I've given this enough thought for today.

If I understand correctly, your modification should work fine as is and I'm thinking your issues are not (directly) caused by the single point mod. So on the 73 harness, there are two black wires that go to the distributor for the points, right? And you have shorted both of them together and then connected that pair to the single wire coming out of the 72 distributor? If that's the case, it should be fine. But, stranger things have happened. Can you put the original 73 distributor back in just to see if the problem goes away?

But I don't want to come off as if I'm poo-pooing the idea. I actually think it's a pretty neat concept to a common problem. So... How would you utilize that Dorman purge valve to accomplish what you were trying to do? Take the screw back out and silicone the cap (with no diaphragm) onto the canister so it doesn't leak. Maybe use the original diaphragm along with silicone to help with the cap sealing, but cut a half inch hole in the center of it first. You want the cap to seal to the canister but you do not want the diaphragm to be able to block off the little hole where you had the screw. One other detail is that you have ruined the metered orifice in the canister by running the screw in, so you would need to use the spare can you picked up instead of the one you had the screw in. So bottom line? Replace the can with the spare (with no screw this time) and put the cap on in some fashion such that it completely seals along the perimeter, but cannot and will not ever block off the hole in the post in the center.

I'm really sorry, but unless I'm missing something, this modification does not work. Sure, it will get rid of your previous vacuum leak, but only because you have effectively plugged all of the hoses. You could have just capped off the vacuum lines at the throttle body and the intake manifold with rubber plugs and the end result would have been the same.

Here's some info on that topic: https://www.classiczcars.com/forums/topic/67864-ignition-systems-analysls/ It's a little academic (and unfinished), but I find it interesting. Might just be me. In any event, I'm hoping the module issues here with @HusseinHolland resolve themselves easily. We can get into some of the deeper details if they don't.

Glad you got the busted off remnants of the old sender unit out of the block. As for cleaning out the threads... The correct tapered tap would work fine. Two things I would keep in mind though: 1) Any metal you take off runs the risk of ending up in your oil galley. Take appropriate precautions. 2) Since this is a taper thread, any metal you take off will end up in the male stub threading in further before sealing. Don't go any deeper than you really need to. Clean it out... Don't make it bigger.

Hahahahahaha!!!!! No, we don't want to see it.

Actually I think it was SteveJ that exhibited naked hostility. Zed, You were properly chastised for not knowing enough ways to skin a cat.

Getting back to clocks and such.... @HusseinHolland, did you try reducing the 2M resistance to see if your clock would start without a push?

Haha!! Of course you do! I think I remember seeing them when I was there.