# 1985 4x4 carb problem



## hunt (Apr 14, 2016)

Hello,
I am new to the site . Hopefully I can get some help with my 1985 4x4 . I have had it about 2 years but have driven it very little. The carb on it is very different than any I have ever worked on before.

The main problem is it seems like its loading up. It idles way to high and when I do get the idle down then black smoke is coming out of the exhaust and it seems to miss just like a motor does when its running to rich.

What are all the electrical wires for that are hooked into the carb?

Please help ? I bought another carb (used) for 75.00 and it does the same exact thing.
I am not sure what motor is in it but I know its a z motor and it has the duel plug setup. Its a 4 cyl.
I will get all motor info if needed but I first wanted to see if I can get any feedback at all from somebody that has some knowledge with this type of carb system ? Thank you


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## OhmsLaw (Mar 29, 2016)

hunt said:


> What are all the electrical wires for that are hooked into the carb?


I'd guess solenoids or heaters or sensors or switches.

Check the resistances between wires with an electronic VOM and record the values in case you have to refer back to them.


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## rogoman (Dec 16, 2004)

The electric wires for the carb connect to the electric choke that's part of the carb. Make sure the choke is operating properly; if the choke is closed or partially closed with a fully warmed up engine, the engine will run very rich and have a tendency to die out. It's also possible the air bleeders inside the carb have dirt in them causing the carb to run rich which will require a rebuild of the carb. Even the used carb may be dirty.


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## smj999smj (Jan 1, 2006)

If it's an 85 720 with a gas engine and 4X4, you likely have the 2.4L, Z24s engine. There was also a 2.0L, Z20s engine, but I think it was only used in the 2WD models. The carburetor is a Hitachi model. It was actually a very good carburetor, but just like anything, if you're not used to them, they appear a bit daunting, especially compared to something simple, like an old, Autolite or Carter 2bbl. 
There were two types, one with the electronic feedback system and the other, without. The system without the electronic feedback system would have a wire to the electric choke and a round, 3-pin, white, plastic connector with wires going to the IACV-FICD solenoid (Idle Air Control-Fast Idle Control Device), which screws into the side of the carb. 
If you have the one with the electronic feedback system, you would still have the choke and IACV-FICD solenoid, but, the harness connector would be bigger and have around 6 or 7 pins in it. You would have 3 wires from that plug going to a square, metal, box, which is a throttle position switch and another two wires that go to the fuel bowl, entering just in front of the air horn. 
There is an idle mixture screw in the base plate (aka "throttle plate") of the carb which, if it's never been adjusted, will be hidden with an aluminum plug, which would need to be carefully drilled out to access the adjustment screw. 
There should be a round, glass window on the fuel bowl cover. If the float is adjusted properly, you will see the fuel inside the bowl and it the level should be viewed in the center of that widow. 
As mentioned, you could have dirt in the carb. You could also have an issue with the IACV-FICD solenoid (some will refer to this as a "fuel enrichment solenoid," its circuit or the ECU. A factory service manual is your best friend when it comes to working on these. Reman carbs are available, but not cheap, usually going for around $450 (new carb from Nissan is twice that much, if it's still available).


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## hunt (Apr 14, 2016)

Wow!
That's a LOT of info ! Ha Ha Thank you.
I can see that this is not going to be a quick fix so I guess I will have to do more research just to begin to understand what I am looking at.

One more question. Between the carb and the intake there is a heater plate of some sort. Is this a vital part of this system? I live in the Mojave Desert and its soooo hot here most of the time.............

Also,i fully understand the carb could be fouled with dirt if not for the fact that my old carb does the same exact thing. High idle and nothing I can adjust will bring it down.
With the key on and engine off I can look into the throat of the carb and see gas dripping into the intake ! My first thought would be that the float was stuck ? Well whats the chances of two carbs having the same problem with the float ? Weird.
I am starting to think in the area of a cold start problem? I don't even know what that is so ......... I am just guessing. I keep thinking about how a carb could access the fuel supply and bypass the float ? I have never ever heard of such a thing but then again I am not sure what a cold start device does sooooooooooo ???? Any ideas ? I am really,really close to saying to heck with it and finding a Weber carb and putting it on. I don't have a clue how I would pass Calif smog though. All I do know is my wife let me buy this 4x4 2 years ago because I told her "it was a investment" but I cannot get it running well enough to sell it ! Ha Ha I really like the truck. I think it has a factory lift and its got roll bars with 4 spotlights . If I was a young kid I would have loved to have it ya know? BUT not if it will not idle at a normal R.P.M. Ha Ha

Anyway,if you have any ideas I would be thankful for the help. I am now starting to really like a injection system. Thanks for the carb info. I will have to read it again slowly... Ha ha I believe my carb has more wires going to that plastic plug so it would be the one with the feedback system but I will have to go check. Thanks


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## OhmsLaw (Mar 29, 2016)

hunt said:


> my wife let me buy this 4x4 2 years ago because I told her "it was a investment" but I cannot get it running well enough to sell it ! Ha Ha


It is no wonder that
"women, they do get weary" - Google Search


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## smj999smj (Jan 1, 2006)

The float engages the needle and seat assembly to turn off the flow of fuel, so it's possible to have a sticking needle and seat; this would come with a rebuild kit (BTW, I'm pretty sure you can still get rebuild kits from Nissan for these carbs, if you're not crazy about aftermarket kits). If the idle stays high no matter what, I would unplug the IACV-FICD soleoid and see if the idle drops. If it does, then you know the solenoid is faulty OR there is an issue with the control circuit. You might want to look at the coolant temp sensor for the computer (not the gauge). 

The base plate heater is to help better atomize the fuel. It's nice if it's working, but not necessary for the engine to run properly. Remember "hot" is relative. It may be "hot" to you in the desert, but it is a lot "hotter" inside your engine.


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