Captain Obvious

I'm still confused, but no big deal. I assume I'm just confused by the terminology. Thanks though!

Well OK. I stand corrected, 50mW IS enough power to heat that thing up! Dave, I'll check my cold resistance too when I get a chance just for another data point.

Haha!! Yep, I remember! Good times!!

Oh, and about this. Great pics and write-up. I went through all of this a bunch years ago and only took a couple pics. I replaced my loose turn signal pivot with a threaded in version I made on the lathe and I cleaned out all the switches and put in headlight relays. Hopefully both of us are done with issues on any of that stuff!!

But that's the problem with DC non-inductive loads. I'm saying that I don't think suppression diodes are the answer. I started typing a whole bunch of stuff about inrush currents, arcs, plasma, and ionization, but worry that we're getting too far off topic and stopped. Let me know if you really want a bunch of details. Transient suppression and mitigation is not an area that I ever specialized in (it's one of the mysterious black arts of engineering), but I just can't picture diodes being an answer for DC loads unless you are trying to deal with the flyback from an inductive load. Sorry OP for the diversion as well. I'll try to keep my mouth shut now!

It sounds like empty bowls to me. Check the float bowl level with a clear tube. Don't just measure something mechanical on the float itself and assume that will result in a correct level. You actually have to measure the level directly. Do you have the little screen filters in the carbs? Maybe they're clogged?

Yeah, that's very true. If I were solving this problem now, I would throw a couple hundred thousand transistors and a one time programmable chicklet at it and call it a day. In fact, that's what I did with my temperature/oil pressure warning lamp. Microcontroller reading a D/A and using digital filtering to weed out spurious false positives. As for the ballast resistor, it has a completely different purpose. They don't want the ballast resistor to change value, they just want it to limit the current to protect the coil and whatever is pulling it to ground. The reason it's necessary is because of the way inductors work. When you first apply voltage to an inductor, it acts like an open circuit. Infinite resistance. Won't allow any current to pass. Then as time goes by, the resistance of the inductor goes down, and it allows current to pass. More and more and more current as time goes on. And in fact, with a theoretical perfect inductor, after enough time, it appears as a dead short. Zero resistance. So the problem is, if there isn't something somewhere in the circuit that limits that current at the upper end, it can reach the point where it gets so high that it will damage something. The ballast resistor limits that upper end of the coil current. You see, when you have points, you really have no idea where the points were when you shut off the motor last time. Points may be open, or points may be closed. If you turn the key on and don't crank the engine, you will quickly cook your coil or your points if you don't limit the current. And the early electronic ignitions systems sit in a stable default state with their output transistors turned on. There is no current limit built into it at the upper end. So the same thing goes there... You could cook the coil if you don't have a ballast resistor. It wasn't until 78 that they started making the ignition modules good enough such that you didn't need the ballast resistor. I haven't played with one, but I assume they did that by building in an upper end current limit into the output stage.

Dave, that's a good question about the cold resistance. That would be good to know. I guess I could check mine too without too much trouble. It's a little bit of a pain to take the stuff out of the hatch area to get to the connector, but if I get that curious, I'll do that. I bet there's a connector up under the dash I could use too if I dug into the wiring diagram. I'm assuming your 3K is not correct. At 13V supply, that will dissipate just over 50mW. I don't think there could possibly enough internal heating at that low power level to change it's resistance. It would have to be uber sensitive, and have an almost vertical knee in the curve. I'm with you... I think you've got connection issues elsewhere.

LOL. That's a great BTDT answer!

I'm not a body guy at all, but from what I thought to be correct, the statement confuses me. It is my understanding that all of the liquid and gelled and putty portions of all the body products are plastic (polyester or epoxy). You can smear plastic resin over fiberglass matt. Or you can smear plastic putty (available with or without fiberglass strands dispersed in it) on without the fiberglass matt. But in the end, you're always using some sort of plastic filler, aren't you?

I'm going to answer in a slightly different way: The only time it would really matter is for a stock correct specimen. And even then, the only cars that anyone really seems to care about stockness is with the 240s. Stock is "nice" for some people for the 260 and 280's, but it doesn't seem to affect the price nearly as much as with stock 240s. So..... Couple that with the fact that the EGR didn't start until the 73 240Z? My bottom line is the only time it would really matter much would be with a stock 73 sale. If you have a 260, or any 280, just do what Mark said and just put the parts in a box for the next owner.

Oh, and BTW, the discussion of bulb filaments changing their resistance dramatically as they heat up reminds me... Sorry for the diversion, but since we're so close... The higher inrush current from a big-ish incandescent load (like headlights) isn't the most gentle thing that can occur to switch contacts. Between that, and the lack of arc extinguishing when you turn stuff off, you can eat up the contacts in the switch even though you aren't switching an inductive load. @ETI4K We were having a discussion some time ago and the million dollar question you didn't ask me is "OK, smart guy... Then if the headlights aren't an inductive load than why do the switches burn up like that? Huh? Why's that?"

No! Own It! But I know exactly what you mean... Off quick, and slowly comes back. I'm sure you nailed it and it's just fuel sloshing onto the sensor.

I bet that's just a slosh quickly dousing and cooling the sender. My DD does the same thing. I always pictured you as that kind of guy. Zed "Danger" Head

Steve, LOL. No. I'm talking about the balancing act between the changing resistances of the thermistor and the bulb filament. I measured the filament resistance of a couple of the 3.4W bulbs from the Z. When cold, the resistance is about 5.4 Ohms. If you calculate the power that bulb will consume when connected to a 12V source, you get about 31 Watts. 31 Watts!!! And the current that would flow through that 5.4 Ohm "resistor" would be about 2.4A!! However, it doesn't work that way. The resistance of the bulb filament increases significantly when it heats up and glows. That's what I meant a while ago about the bulb being a PTC. To show this effect, I connected the bulbs to a 12V source and measure the current draw while the bulb was lit. It was 220 to 240 mA. And if you back calculate the filament resistance, you find that the resistance has increased about tenfold from 5.4 Ohms to about 50 Ohms. So as the resistance of the thermistor decreases (allowing more current flow), the resistance of the bulb goes up (disallowing more current flow). That's the balancing act I was talking about. It's just a light bulb and a thermistor and it's giving me a headache. HAHA!!

I want to hear Steve's explanation about the whole balancing act and competing factors here... But in any event, it sounds like you DO have the correct bulb in there, so I think we're back to the thermistor.

I had originally thought there was simply some dyslexia going on here, but now I'm not so sure... The original bulb spec is 3.4W, but the one in your pic (and part number) appears to be 4.3W instead. If that bulb really is 4.3 instead of 3.4, that might be part of the problem. Do you have another (known to be correct) bulb you can toss in there just to see what happens? My original bulbs were Toshiba A12V3.4.

Ha!! Made you look! So the only thing they can muster is "It's resistance is different". Not much help! The whole thing is a balancing act... The thermistor in the tank is a NTC and the bulb filament is a PTC. You need the current through the thermistor high enough to achieve the desired power dissipation such that there is self heating when not submerged in fuel, but never enough power to damage it. And when the thermistor does heat up and it's resistance drops, you need the resistance low enough to get the bulb filament to glow.

I got no silver bullet. The only explanation I have is what you already mentioned... Sounds like the thermistor is not quiiiiite right for the application. CLOSE, but not enough headroom for tolerances and environmental stressors like ambient temp and system voltage. And as Zed mentioned, why it only happens when the engine is running is probably because the system voltage is higher then. That extra volt-n-a-half matters. Thermistors come in all sorts of base resistances and with all shapes different curves. For this application, you want one with a "knee" in the curve as opposed to linear, and you want the knee to be at the correct temperature. I'm thinking that it's too close to the limit most of the time, and the combination of ambient temperature and system voltage (when the engine is running) puts it over the edge. @Dave WM, Did you find any specs at all about the thermistor? Anything at all? I didn't look at any of the FSM's, but I bet you did. I wonder what thermistor ZCD picked for their unit. And why.

Haha!! Could be! I'll crawl back under my same as it ever was rock now.

@siteunseen, what's the deal with the goofy new pics? You get a new toy or subscription to something?

This recent thread: https://www.classiczcars.com/forums/topic/64260-240z-hls-30-42277-restauration-colombia-southamerica/?do=findComment&comment=603098 Includes some pics of what looks like the same transmission: Kinda dark inside the bell housing to get a real good look at the pivot ball post, but maybe @Mazinga Z would be willing to take a closer pic for you.

I find the parts documentation confusing. Even though the new pivot number says no interchange, note that it DOES list that it superseded the old number. I did some internets searching for info on the part numbers and turned up very little about the old one. I agree that it would be very enlightening to see a pic of the old pivot next to the new one.

So it's a bummer when your old un-rebuilt carbs are in better shape than "rebuilt" ones you paid (I assume) good money for. That throttle shaft is a disaster. I kinda wonder what other issues are lurking with those "rebuilt" carbs. I guess if they work OK (the rear one at least), one could assume any other mishandlings are minor enough to keep using them. Only suggestion would be to make sure you check the float bowl levels.

That's a good video. Thanks for that. So good luck with it, regardless of which way you decide to proceed.