Captain Obvious

Terp, Awesome. Thanks for the great pics. And your number matches the Hitachi valves I have here. So assuming site's 72R valve comes in at the same dimension as what's in your pic, here's a summary of what I have so far. Most of this is old news, but just to put it into a form that my little brain understands... The float valve for the 72F should be 20.5mm. That is 2mm longer than the previous years and Datsun adjusted both the length of the float ears and the depth of the valve recess of the 72F lid to accommodate that change. The intent seems to be "They wanted the front carb float level to be approx 2mm lower than it used to be in previous years." The float valve for the 72R should be 18.5mm, and it's interesting to note that this is the same length valve Datsun used on the previous round tops in 70 and 71, but a different part number*. And again, Datsun adjusted both the lengths of the float ears of the 72 R lid as well as the depth of the valve recess to change the float level. The intent seems to be "They wanted the rear carb float level to be approx 2mm higher than it used to be". *An interesting side conversation would be... So if the float valve for 72R was the same length as the previous years, why did Datsun bother to change the part number? Why not just spec the 70-71 valve for use in the 72R lid? I've got two theories about that: First is that there's a note in the EF section of the 72 FSM about how they changed from a hardened steel tip to a rubber tip for the sealing of the float valve. Second is that I've got (what I believe are) early 70 valves here and they have a different through hole. The 70 valves I have 2.0mm through hole, while the later 72 valves have a 1.7mm through hole. So while the length may be the same, they may have sprung for a new part number because of those changes. However, despite those changes, it seems to me you could use the same valve for the 70-71 round tops and the 72R. The 72F is still the outlier.

@Terrapin Z, @siteunseen When you guys get a chance, could I trouble you both to take a caliper measurement of the short valve going all the way to the top of the valve? Also, do your short valves have the "R" stamped on them? Looks that way in the pics, but just checking.

Well I guess I'm going to test that statement about the new aftermarket valves being the same front and rear. I just put in an order on rockauto for rebuild kits for the 72. They call out two different part numbers for the kits and make it clear there is a different one for front and rear. So I'm going to soon see why they spec different kits for 72 F and R. If it's not the needle valve length, then I don't know what it's gonna be. I guess I'll let you know in a little while when the kits get here!

Oh, and it's clear to me that Datsun really messed around with stuff in 72. The float valves are unique, the lids are unique, everything is different than the previous years. It looks to me like they were chasing minutia. Some engineer realized the slight geometry differences between front and back carb bowls when they mounted on the car and convinced management he could make it better. I'm thinking they should have just left well enough alone. Also makes it clear why I was having a hard time getting these carbs right... They're all kinds of wrong inside from previous owners.

Yeah, I'm measuring including the rounded top portion. Essentially I'm interested in "how far does the valve stick out of the bowl lid", and that includes more than just the hex portion. So I'm measuring everything from the sealing washer surface to the top of the valve (not including the movable internal bits). Like this: So this is my (cracked body) 72F valve. I get .806 (20.5mm), That makes sense since the TSB mentioned earlier says they lowered the bowl level for the 72 front carb by 2mm. Both the valve and the bowl lid ears got 2mm longer for the 72F, so all the numbers line up to support that: So when your eyes get back into focus, let me know.

You don't need a welding rep. You need a metallurgist and an automotive transmission engineer.

You want the gears to be hard enough to be "tough" and "wear resistant" but not so hard that they're "brittle". And you want the heat treat to be predictable through the part. Welding heat would definitely take the metal above the temperature where the original heat treat would be changed. And without knowing how it changed, it's risky. After welding, it might be harder, softer, or exactly the same. It's all a crap shoot and the only safe thing would be to start over. And even that comes with issues because you don't know what the original spec was. I just see the whole thing as risky. I mean, not that I've never done risky stuff, but, you know...

Thanks guys for the float valve measurements. I did measure from the base all the way to the top of the valve. I figured overall length was the important parameter. I would assume that the dimension from the end of the hex to the top of the valve would be pretty consistent within the same manufacturer, so I ought to be able to convert your measurements to overall. I wouldn't complain, however, if one of you guys would measure the length from the bottom of the hex to the rounded top of the body. Just don't catch the little retainer spring under the caliper jaw. Easy peasy. Also, I found a stock long valve here. It's cracked (so it's unusable), but I will check that one too. Thanks!

Haha!!!

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?