Zed Head

I think that started design life as the heating block for the AAR, in the early 280Z's. But it looks like Nissan added some function with that vacuum switch.

My past problem only happened after the engine got warm. Apparently there was enough clearance for the blade to close until things got hot. Took me quite a while, messing with springs and poking at the linkage while it was cold (because working on a hot engine in the summer heat sucks), to realize that it was a hot engine problem, that had nothing to do with controls that should be affected by heat. Just wanted to repeat that. Finding repeatable problem conditions can be hard but finding them makes the solution easier. Beside that, working on the BCDD is a pain, from the FSM description. You're supposed to get the car up on blocks and run the car in gear and measure things. Better to have a friend ride in the engine bay.

You should give a little more information about your car than "Z". Apparently it's a 280Z since it has injectors. The noise is called "front-fire" or intake popping among other labels and it is pretty common with the 280Z's. Not clear why but the EFI system runs lean in some cases. The best fix that many of us have used is to cause the system to add a little extra fuel across the air flow range, using extra resistance on the coolant temperature circuit. Atlanticz has a great description. http://atlanticz.ca/zclub/techtips/tempsensorpot/index.html BUT. This is a fix for after you've confirmed proper fuel pressure, and ignition timing, and valve lash, etc. I'd give it a very thorough tune-up first.

It's not usually necessary to adjust the BCDD. Just saying. Here's one last thing to check before you get in to that. You said the dashpot seems slow. I'd mark where the dashpot is set now and screw it back out to where it has little effect. If the BCDD is bad, the problem will still be there. If not, the problem will go away and you might have a new one. The dashpots I've had have been creaky and slow and worn and sticky. They did need adjustment.

It's in the Excellent range - https://www.hagerty.com/apps/valuationtools/1970-datsun-240z

Here's another but the guy doesn't know what he wants for it - https://bend.craigslist.org/cto/5957114887.html

Here's the Oregon listing. Corvallis. Don't know why he skipped over Portland. Edit - actually he might be close to Portland and just went north and south. I think I've heard of a car like this in Newberg. https://corvallis.craigslist.org/cto/5961147455.html

Doesn't look terrible. Price seems close to right. https://salem.craigslist.org/cto/5957162867.html

Those are u-joint half-shafts. You'll have all of the parts you need to swap the R200 in, without extensive work. Your 240Z half-shafts will work, if you are buying the parts separately. Although a spare set of half-shafts isn't a bad idea. Get a zerk fitting and regrease the u-joints before installing, if they have the caps over the zerk holes. I think that you might want the diff mount also, just leave it bolted to the diff. Although it's probably rotten.

CV axles didn't show until about the 1980 280ZX. Maybe 81. Got pictures? Not clear what you're working with. If you meant 280ZX 2+2 then you could do a hub axle swap. The 240Z and 280ZX used the same spline count axle and size at the hub. There are writeups out there. BUT. The 280ZX doesn't use a mustache bar. So, back to not clear what you're working with.

It's under the plastic kick panel. The screws are hard to get to. The pedal in this picture is the clutch pedal. I circled the connector.

Could be you just need a tuneup. I've personally wasted a lot of time, and have seen others do the same, looking for solutions to a problem that was solved by new spark plugs. Your list says that the plugs were already dirty when you put RCB's ECU in. The ignition module is weaker than later models but still, it's as good as points. A tuneup, with new plugs, should get you back to baseline. An improved ignition system will get you more time between tuneups. Get back to baseline before swapping the big money stuff. Seriously, I really have spent a lot of time on a problem, then put new plugs in and it went away. (I felt like an idiot. No offense).

Apparently the BCDD can cause RPM to hang high. It's described in the Emissions chapter. I had a problem with a hanging throttle blade due to gunk in the throttle body bore. Nissan actually put out a Technical Service Bulletin about and had a fix involving cleaning the throttle body and rerouting the PCV hoses. The dirty blowby from the crankcase fouled the blade. In my case, it only hung up when the engine was warm. I fixed it with carburetor cleaner and a little abrasive pad work where blade seats when closed. It only takes a small opening to let a lot of air through. You can distinguish the BCDD problem from the throttle blade problem by pulling the throttle pedal up with your foot when it happens. If it goes away then it's a blade opening problem. The BCDD lets air by when the blade is closed so that cause won't be affected.

I like the points suggestion. Sounds like the OP really just needs to give it a good tune-up. That would cover points, condenser, valve lash, timing, etc.

Do you have some links, I'm searched out. The thing is, when it comes to boiling or vaporizing, the low boiling components go first. They don't wait for the high boiling components, if more high oilers are added. There's no averaging down. Fuel is a blend of vapor pressures.

Thanks. I couldn't find the actual reference to using diesel to change vapor pressure but I did find another article that kind of shows he's just a guy like us, pulling together odds and ends and making assumptions. http://fifthaveinternetgarage.com/pdf/RefiningModernGasoline.pdf " Ethanol alcohol attracts water. It picks up moisture throughout the fuel system. In the early gasohol era, this sensitivity to water led to problems because service stations often had water in the bottom of their underground tanks. Officially… the petroleum industry is well aware of these considerations and companies using ethanol have implemented procedures to eliminate moisture in underground storage tanks. It is best to check the fuel you buy to see for sure if there is water in your fuel, especially if you are going to place your antique vehicle in storage for longer than 60 days. The addition of 10% ethanol will typically contribute 2.5 or more octane numbers to the finished blend. The addition of ethanol increases vapor pressure by up to 1.0 psi although refiners may make other alterations to limit vapor pressure to comply with federal regulations. Ethanol is approximately 35% oxygen (which is part of the source of vapor lock when we use modern gasoline in our antique vehicles) so a 10% blend would contain approximately 3.5 weight percent (w%) oxygen that improves combustion properties. Ethanol is often confused with methanol. These two alcohols have distinctly different characteristics. Unlike ethanol, methanol is very toxic. Ethanol provides better water tolerance and better fuel system compatibility and contains less oxygen than methanol. Methanol causes a significant increase in volatility (which is why it is used in race cars and performance applications) while ethanol results in only a slight increase.

It might be gone by now, it's been a while. I meant to get out there but it was either too cold or too wet. Should be above water, it's on the high side, Row 18. Anybody recognize it? Posting mainly for the color. It's got one of those 2.7 liter engines. https://row52.com/Vehicle/Index/JN1HZ06S7BX403214 @Mark Maras

Is your throttle return spring intact? They rust and break. There's a second spring on the throttle body itself but it's not very strong.

77 still used the three part fuel rail, consider using a 78 or a ZX rail, or aluminum. Search "heat soak" and/or "hot start" problems before you get too far along. You might break some thermostat housing bolts also. They tend to rust in place and break in the middle though. Injector mount bolts break too. And exhaust pipe flange studs. Lots of breaking and stuckness. Check the manifold surfaces for flatness. Consider just having another complete engine ready to swap in. With a 5 speed. Just an option.

77 still used the three part fuel rail, consider using a 78 or a ZX rail, or aluminum. Search "heat soak" and/or "hot start" problems before you get too far along. You might break some thermostat housing bolts also. They tend to rust in place and break in the middle though. Injector mount bolts break too. And exhaust pipe flange studs. Lots of breaking and stuckness. Check the manifold surfaces for flatness. Consider just having another complete engine ready to swap in. With a 5 speed. Just an option.

I've had a similar thought but with regard to detonation. Another plus would be more energy per unit volume. Seems like the pros would have had to think of it. One downside I would guess is that diesel needs high pressures to burn fully, I think. CR's on diesel engines are much higher than gasoline. Probably would dirty the plugs a lot faster. And smell bad. I'm not sure the idea pans out fully though. The high vapor pressure components are still in the formulation and they would "distill" or "fractionate" out. The fuel is a blend of molecules, so all you'd really end up with is a lower concentration of the unwanted molecules, but they'd still bubble and boil. It might be the same for my detonation argument. It makes sense from an "averaging out" view, but I don't think that's how the fuel works. An easy experiment though. Do you have a name or author for the article?

She has the problem of sporadicity. Checking for spark works when the engine won't start, but won't really help when she's rumbling down the road. Always good to have a plan of action in place though, for when the problem happens. And it's the rumbling that makes things not so clear. The engine is running, just not well. That's where a wire wiggle might show something.

Saw your post on another forum and thought of something that might make it easier to actually do something. You can leave the metal fuel rail in place and just disconnect it, running a rubber hose to replace its function. If it has a positive effect then you can decide whether or not to remove the metal rail. All you need is some hose and a screwdriver for the hose clamps. No need to unbolt anything anything, just pull a hose end off and replace it with another hose.

Just trying to help. Honest. I see the tape now, but I'd take the flares off and show the car without them. I'd show the passenger side of the car also, I always get suspicious when parts of the car aren't shown. Might as well post the eBay link too. Is the big red dot a decal? I'd take the decals off. No offense, I know you're really showing your vision for the car, but buyers would rather see a clean slate. Looks like a decent car.

The running rich (black plugs) and the sudden dying are typical signs of a bad ECU OR a bad ECU connection. People have reported wiggling the ECU connector while driving to fix it. Maybe the fix of replacing the ECU really just fixed the connector issue. And it's come back. Might try wiggling the ECU connector, or pulling it off and putting it back on, just to see if it has an effect. The rumbling might just be the engine loading up with fuel and fouling a few plugs. Running on fewer cylinders for a while. If wiggling the connector has an effect I'm not really sure what the long-term solution is. But it would be a clue. Could also be that a second ECU has gone bad.