Carburetor component identification - elec devices for Z24(s) engine

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Carburetor component identification - elec devices for Z24(s) engine

Postby spddm0n » Thu Apr 25, 2019 11:05 am

Hi all -

I just picked up an '85 720 the other day, and I'm tackling an issue with the carburetor...specifically, the electrical components that "should" be connected on the carburetor via the large 6-pin electrical connector. I've looked at a variety of threads on these carbs and I've not been successful correctly identifying each of the components. Various people, manuals, and Nissan OEM language, all see to call these devices something different. I'm hoping to get some clarification.

The carburetor I have on the truck is NOT the OEM Nissan carb. It appears to be a new eBay $85 special, installed by the previous owner, in attempt to get the engine to pass emissions. This carb is missing a few of the electrical devices the OEM carb had, so I expect I may need to replace this unit with another, in order to pass emissions.

I found a wiring diagram for a Z24 engine, but I'm not sure of the year it was for. It identifies four devices, that are likely connected to the carburetor, but I'm not sure what is what. I'll post that image below, if I can figure out how to host it.

The items identified in the wiring diagram are:
1. Auto Choke Heater. (1) wire. Blue (L).
2. Air-Fuel Ratio Solenoid. (2) wires. Yellow with black stripe (YB) and White (W).
3. Throttle Valve Switch. (1) wire. Green with white stripe (GW).
4. Anti-Dieseling Solenoid. (2) wires. Red (R) and Black (B).

First, there is (supposed to be) a two wire electrical device on the front of the carburetor, above the float bowl. What is that device called? It appears this might be the device with the Yellow-Black and White wires, but I can't confirm. If so, it must be the Air-Fuel Ratio solenoid. Is this commonly called something else?

Second, the device that is visible from the passenger side of the carburetor (technically screwed into the carb from the back-side though), appears to have a Red and black wire. Is this the Anti-Dieseling Solenoid? If so, is that referred to as the IACV-FICD solenoid? I looked up an FICD solenoid, and that refers to a device that causes the idle to rise when the A/C system is activated. I don't have A/C, so what is this device? Are the IACV and FICD different devices? Are the combined on some models? If not, where would I locate a separate FICD device on A/C equipped models?

Third, there is a single blue wire attached to what appears to be an electric choke on the back-side of the carb, at the top. Is there a difference between a auto-choke and an auto-choke "heater"?

Last, there is a Gree-White wire on the connector, but nowhere to connect it. I looked at some other pics of the hitachi carb and it appears there is a small device on the back of the carb, nearer the driver-side. Is there a throttle valve switch that is supposed to be there? Is that commonly called something else?

I'm wondering if I can purchase an affordable carburetor (not a $475 unit) that has all the required connections, or if it's reasonable to expect I could get this engine to pass emissions with a more basic carburetor, like the new unit that was installed.

I am also still having trouble correctly identifying some of the various vacuum components on the engine, and ensuring the vacuum lines are correct. I'll post a new topic for that though.

Thanks for any help that can be offered!

Wiring Diagram ... wiring.jpg

Images of the carb I have on now ... .l4275.c10
Last edited by spddm0n on Thu Apr 25, 2019 11:09 am, edited 1 time in total.

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Re: Carburetor component identification - elec devices for Z24(s) engine

Postby DA82KC » Thu Apr 25, 2019 9:41 pm

What you are supposed to have is the electronic DFP? 384 hitachi carburetor. It would have a mixture control solenoid in the place of the main jet. The carb you have is a cheap eBay federal or Canadian variant as mixture control was not a feature of Canadian models at all on the 720 run and the plug typically sold with those carbs matches the Canadian harness plug to the carb.

The carb you have could probably be made to work, but if you live in an area requiring a smog inspection, it will not pass. Sadly, if you must have a factory carb, you will need to obtain one.

Most folks prefer to dispose of the factory carb and replace them with Weber DGV carbs. Redline sells kit K646 which gives you all the parts needed to perform the retrofit. Should you go that route, and your locale requires a visual emission inspection, it will fail the visual for the same reasons as the carb you already have. But, should you not need a visual test, it will likely pass the tailpipe emissions test and will probably run better.

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Re: Carburetor component identification - elec devices for Z24(s) engine

Postby spddm0n » Fri Apr 26, 2019 10:08 am

Hey, thanks for the reply! Yeah, emission regulations here are pretty strict. Visual exams are a bit more lenient, but it will be put to operational test on a dynamometer. I should probably check on the visual inspection for a carburetor though. I've never tried to pass emissions with a least not in the last 30 years. :)

Interesting about the webers...that would be a fun option. :)

Is the mixture control solenoid in the front of the carb? Is that what Nissan is calling the Air Fuel Ratio Solenoid?

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Re: Carburetor component identification - elec devices for Z24(s) engine

Postby Gr8Guyn08 » Sat Apr 18, 2020 10:28 am

To expand a little on what DA82KC said.

The Federal and Canadian carburetor has two electrical devices on the back of the carburetor. The electric choke and the anti-dieseling solenoid. Each device has one wire with ground coming through the body of the carburetor. I believe that the connector is only 3 pins.

If you have a carburetor with a 6 pin connector that is going to be a California carburetor. There is also a "computer" module that I think is mounted under the passenger seat. (I have a 1983 Federal and not all that familiar with the California model).

The anti-dieseling solenoid shuts off the idle port when you turn off the engine. It is what you describe that is screwed into the back of the carburetor that you can see from the passenger side of the truck. These solenoids are no longer available and have a history of failing. I believe that the failure is that the wire coming out of the solenoid breaks off at the solenoid body. The solenoid is not actually necessary if you have a manual transmission. The engine tends to only diesel when it is quite hot and with a manual transmission you can just push on the brake, put the truck into gear and let off the clutch and stall the engine.

The air conditioner idle bump up is actually a vacuum solenoid and is mounted on the back of the carburetor on a bracket. When the air conditioner turns on the vacuum solenoid pushes down on the throttle just a bit to bump the idle up a couple hundred RPM. On the California carburetor all that may be controlled through the mixture "computer", don't know.

A couple of years ago I was having carburetor problems and looked into the Weber conversion. From what I remember there was a lot of stuff about they would not meet emission standards.

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