Zed Head

Since letting a little more air in through the AFM doesn't increase idle RPM that seems like a sign that you might have a big vacuum leak in the intake system. The engine needs a lot more air through the AFM to add more fuel. Unmetered air leaning things out so that the engine can't run. Do you have all of the PCV hoses properly connected and sealed? A picture of the engine would tell more than a picture of the car. Looks like fun. Also possible that you're not adjusting the correct screw.

CO mentioned valving. I looked around and found a mention of residual pressure valves. That could be a reason. I think that the topic has come up in past discussions, I had forgotten about it. You can hold pressure on drum brakes because there are return springs. You wouldn't want that on the front. Makes me realize that it could be a possible cause of dragging brakes, mixed-up lines. Makes you wonder though if the quality level of a reman master cylinder is really up to the level of controlling residual pressure. Another neat test bench factor to consider. Or just do F and R. "tandem master cylinder" is the search term to use. http://www.britishv8.org/Articles/Tandem-Master-Cylinders.htm "Another issue when selecting a tandem master cylinder is whether it comes with one or more internal residual pressure valves. On an OEM master cylinder designed for a car with rear drum brakes there will sometimes be a residual pressure valve in the rear brake circuit to maintain a small amount of pressure at the wheel cylinder seals. The amount of residual pressure varies from one design to another but typically is between 6 and 25psi. Disc brake calipers may or may not need a residual pressure valve depending on their design. A 2psi residual pressure valve is often recommended for aftermarket disc brake calipers."

I looked in to cavitation a little farther and also came up with aeration. This would be caused by a leak in the suction side of the pump. The pump is above the level of the oil so you need a solid column of oil in the pickup tube to keep the pump full. If there's a leak in the tube or at the pump's suction side it will pull air in along with the oil. So, you could have an obstruction or you might have an air leak. Not sure but you might be able to rig something up at the oil pump inlet to see if the tube is pulling air along with the oil. I don't have a mental image of what would be involved there. Pretty interesting stuff. https://www.machinerylubrication.com/Read/30768/cavitation-or-aeration https://www.machinerylubrication.com/Read/28767/gear-pump-cavitation

Might help to have an illustration of the oil path to ponder. Pressure is caused by resistance to flow. Flow starts at the oil pump. You said that you installed a new oil pump, but who knows about its quality. The oil pump has a relief valve that could reduce pressure. The oil filter area has a relief valve but flow will still be resisted by the main bearings and the restrictor at the supply to the head. So that bypass doesn't really matter. Hard to know how much oil could pass through that restrictor to the spray bar. I think that I saw it in one of your pictures. And, apparently, some engines have another supply passage to the head at the front. It's not shown in the illustration but I have a vague memory of reading about it. A thought that just occured - the fact that pressure reduces at higher RPM might be caused by cavitation. Which could be caused by a restriction in the supply to the pump. So, it kind of circles back around to the pickup tube. Maybe you got a gasket on backward or something. The pump just moves volume. Pressure is caused by restriction.

Actually, the hydraulics of the system mean that both ends get the same volume for the same amount of stroke. Might just be that the F and the R are there so that the mechanic knows where to put the reservoir.

It would be fun maybe to set up a bench testing unit to move fluid in and out of some sort of device. Maybe some graduated cylinders so you could see the rate of flow. I wonder if there is some sort of service bulletin out there with some words about the switching of the reservoirs. Maybe something in Wick Humble's book or one of the others. I don't have my books handy. Nissan's FSM's usually have short explanations for the functions of the various components. This is all I find for the 1972 master cylinder.

It's in the thing...

Here's a red one that made it to $35,000 in November of 2020, but did not sell. Not sure the market is better now. https://bringatrailer.com/listing/1971-datsun-240z-253/ https://bringatrailer.com/listing/1971-datsun-240z-159/

I'm not sure it matters though for function. It's just a bigger reservoir.

Here's the drawing from the 1972 FSM. It shows the big reservoir up front and shows the lines through the warning switch. No drawing number though. This from the very same chapter. Seems reasonable to guess that it's an old picture from 1971.. BUT, I opened up what is supposed to be the 1971 FSM and it shows this.

Is this the current problem? Or is it still doing this? Can you summarize what you're trying to fix now?

Don't forget valve lash. It's the very first thing mentioned in the tune-up chapter. Very important.

It might be the typical "lean" problem with the EFI systems. You can add resistance to the coolant temperature sensor circuit and fix it. Link below. It could also be clogged injectors. When I got my car it had been sitting for a while. The injectors were unbalanced, some were under-squirting by quite a bit. http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html

Your picture is the warning switch right? Anyway, looks like fun.

The 75-77 models have a screw panel for the connections. 78 is the only one with the plug connector. I think that all of the plug connector Z ignition modules are the same. The eBay price is stiff competition though, compared to what they used to go for. The picture looks right. Wonder where the warehouse of old new ignition modules was, that these Spark people found.

I had another thought about the brake check warning lamp switch. It could allow a transfer but I don't know why it would be one way. My first post was on target I think. The seals push one way and let fluid slip past the other way. Easy to check. Good luck.

The ignition module is by the fuse box. They're expensive. I found an eBay ad with a picture but I have no idea where these guys would get new modules. Also don't know if the electronics still age when not used. Don't get carried away. Only posting this for the picture and for anyone else who might need one and want to take a gamble. Seems too cheap to be true. Put "NEW - OUT OF BOX Ignition Control Module For 1978 Datsun 280z 2.8L S30" in the eBay search box. https://www.ebay.com/

Seems like the front seal is installed backward, or one of the middle seals. It's pushing fluid from the front of the cylinder to the back on the return stroke. Easier to imagine with a picture.

That DC car could probably be flipped on BAT for a few thousand profit. Not many pictures of underneath but the battery tray and the few that are there look pretty good. Here's the text. Somebody's probably going to buy it soon. p.s. edit - forgot this part - "1971 Datsun 240z - $16,200 (Falls Church)" "1971 Datsun 240Z HLS30-35788 Northern Virginia Parked in a garage since 1985. Car is carrying the original motor, unmolested, with its E31 head and four screw carbs. Engine turns over, have not tried to start it. 48k showing. Some prior body work evident, exterior paint is not original. Engine bay appears to be original paint and still has the 919 Paint code sticker (yellow). Tires are Michelin XWX I believe from 1980 if I'm reading the sidewall correctly. Series 1 center console, but Series 2 gauges, B-pillar trim, rear hatch, steering wheel, and valve cover. Interior is fairly all there. As far as the rubber floor mats, the underlay, the carpeting, and most of the interior plastics go. Dash is cracked, seats are deteriorated. Some spares included, which includes new seat covers and some front carpets. Two hubcaps. Clear Virginia Title"

@Terrapin Z probably has a used one. Next time take two screwdrivers and lever the wheel off using the distributor body. Be careful with the aluminum.

Here's something for 240260280 Blue. Not music though.

It's a very common problem. Search the forum for smoke machine references. I think that Zs-ondabrain had a good thread going about it. Smoke the inside of the car and look for leakage. Bad gaskets around the taillight housings is another big one. They dry up, shrink, and crumble away. Did a quick search and found a reference confirming his method. Turns out it was actually watching the smoke come in. I assume that either way works. I think the smoke is oily though so their way is probably best. Also, people turn the lights off and shine a bright light on the inside and see where it comes out, or vice-versa. Don't overlook holes in the firewall. Cables, hoses, etc.

Like the finger? Buyers better hurry...

What is the tachometer needle doing when it's smoking and running poorly? Does it match what you hear from the engine? 800 RPM is pretty low. Might be the ignition module going bad. That will usually show signs on the tachometer needle. Could also be the throttle valve switch (aka TPS). Might be stuck on full throttle. 27% extra fuel. Also could be running rich if the fuel pressure regulator diaphragm is cracked. Remove the vacuum hose to the FPR and see if is wet inside. It should be dry. Page EF-15.

I don't know that there are that many Vintage Dashes out there to evaluate. I'd also bet that many of them are sitting in their boxes waiting for the rest of the car to get done. You might be doing them a favor by pointing out this problem. It's not clear who you've been talking to and the details. The part about the refund is new. I agree that somebody screwed up on the trimming of your two dashes. This is the best place to discuss it. They need to reply. @theguppies