85 King Cab ST start up idle

[Messi720D]

So I currently put on a cheap amazon $85 buck carburetor on my 85 king cab ST 2.4  everything seems fine but I did notice high idle around 2k rpm when cold start it come down to about 750 800 rpm after warming up, but let's say I turn it off for about 15 min or so I go to start it up it idles right back up to about 2k, I figured it would be warmed up by then temp temp is about 170 when this happens, even if I'm just loading up on gas any ideas ? Or help 

[powderfinger]

Does the idle drop back down as soon as you tap the accelerator pedal?

[datzenmike]

Next time look at the choke flap position. If it's on even partly after only cooling down for 15 min it may be set too rich.

[A guy named Rick]

9 hours ago, powderfinger said:

Does the idle drop back down as soon as you tap the accelerator pedal?

I second this question

[DwayneOxford]

I got one too, had to do considerable tweaking to get it working right. Accel pump quit, check ball was lodged in hole. Got it out, measured, got my check ball drawer out, found one bout .030 bigger, dropped it in and pumping agin.

[Messi720D]

On 5/11/2023 at 4:55 AM, powderfinger said:

Does the idle drop back down as soon as you tap the accelerator pedal?

No not really it just stays high idle until it warms ups then the rpm drops down, but its annoying i go pump gas or shut it off for 5-10min or so it idles like if it was cold start but eventually comes down to normal idle 

[Messi720D]

On 5/11/2023 at 6:23 AM, datzenmike said:

Next time look at the choke flap position. If it's on even partly after only cooling down for 15 min it may be set too rich.

i have to inspect the choke flap haven't done that will see what i find 

[datzenmike]

 

Usually you can loosen the three screws and turn the choke adjustment to the right (lean) but later Z24 carbs are riveted and set at the factory. I had one and drilled out the rivets and used self tapping screws. 

[Messi720D]

2 hours ago, datzenmike said:

 

Usually you can loosen the three screws and turn the choke adjustment to the right (lean) but later Z24 carbs are riveted and set at the factory. I had one and drilled out the rivets and used self tapping screws. 

I took a quick look this morning and looks like it does have screws to adjust i will work on it this weekend i did notice it gets quite hot by blade terminal and center of choke mechanism. is that normal i know my other carbureted cars get warm but not hot  

[datzenmike]

It's got a heater inside and it's not original so who knows? This is what $85 get you. An original dealler replacement carburetor would be $650- $800 to replace.

[Messi720D]

18 hours ago, datzenmike said:

It's got a heater inside and it's not original so who knows? This is what $85 get you. An original dealler replacement carburetor would be $650- $800 to replace.

Yep lol I'm going to rebuild the original carb first time ever doing so, should be fairly easy, and the cheap carb adjusted toward lean and much better doesn't idle up to crazy and does do it after a few minutes 

[DwayneOxford]

If it's got the thick 6 screw bypass valve you DON'T want to take out the 3 long screws that hold it to carb. They are only 5MM and will most likely twist off.

17 hours ago, Messi720D said:

Yep lol I'm going to rebuild the original carb first time ever doing so, should be fairly easy, and the cheap carb adjusted toward lean and much better doesn't idle up to crazy and does do it after a few minutes 

 

[Yinzer]

 My 86 has that $85 Chinese carb on it as well. The PO put it on and also removed ALL of the Emission Control crap on it and everything around it. 

 

 I had a helluva time getting my carb to act right and idle right. I still kinda wonky... but it works.

 

 Does your carb still have all the Emission crap on it ? The carbs on these rely heavily on all the emission stuff to work right. The vacuum valves, temperature sensors and all the rest.

 

 Also, I had to adjust this little screw on my choke shaft to get the butterfly to close right.

 

Edited May 15, 2023 by Yinzer
Because.....

[datzenmike]

Actually I've found that the emissions systems needs the carburetor to work right. Carburetor has two ported vacuum sources one for the EGR, one for the vacuum advance and the purge signal for the charcoal canister. California carburetors have a vent hose to collect evaporated gas fumes from the float chamber and direct them to the charcoal canister. Other than these there is nothing sent to the carburetor from the emissions system. I would definitely keep the charcoal canister working. It has zero effect on running. I would also keep the PCV valve system connected and working. It's important to keep the stock air cleaner in order to keep the ATC, air temp control functional. This does have a beneficial effect in cooler weather by keeping the inlet air temperature regulated to about 100F all year round. ERG and vacuum advance delay can go. You can keep the AIS functional as it adds oxygen rich air to the exhaust manifold to help the catalytic converter burn off emissions. It's down stream from the engine so has no effect on performance and running.... or remove it all and the cat. 

[Messi720D]

1 hour ago, Yinzer said:

 My 86 has that $85 Chinese carb on it as well. The PO put it on and also removed ALL of the Emission Control crap on it and everything around it. 

 

 I had a helluva time getting my carb to act right and idle right. I still kinda wonky... but it works.

 

 Does your carb still have all the Emission crap on it ? The carbs on these rely heavily on all the emission stuff to work right. The vacuum valves, temperature sensors and all the rest.

 

 Also, I had to adjust this little screw on my choke shaft to get the butterfly to close right.

 

Yeah i left everything hooked up for most part only thing that acts up is idle when A/C is on but turns out the vacuum line that works with A/c switch system was not plugged in, i will take a look at it to day 

[datzenmike]

There should be an 'idle up' solenoid for when the AC is on.

[720_Jeff]

Fast Idle Valve, think that is what they call it on the 720's parts list.  Can't seem to find it on Nissan Parts Deal.

 

Its usual location is on the firewall, drivers side.  One vacuum line going to it.  Forget what is coming out of the other side of it.

Here is a picture of it and location, right next to the hinge for the hood.

 

[datzenmike]

The idle up solenoid is mounted on the cowl and when on or activated by the air con being turned on passes a vacuum signal to the actuator on the carburetor that holds the throttle from closing to normal idle. There should be two vacuum lines to the solenoid. One back to the intake and the other to the actuator on the carburetor.

[Messi720D]

On 5/16/2023 at 6:13 AM, datzenmike said:

The idle up solenoid is mounted on the cowl and when on or activated by the air con being turned on passes a vacuum signal to the actuator on the carburetor that holds the throttle from closing to normal idle. There should be two vacuum lines to the solenoid. One back to the intake and the other to the actuator on the carburetor.

yeah i didn't see where the vacuum hose was attached to on the OEM carb, and i need to see if this after market is set up for a port on that carb actuator i will take a look its not crazy hot here in Arizona but its definitely getting warmer, its always cool seeing an old truck with good A/C here in Phoenix      

[datzenmike]

It doesn't connect to the carburetor. The vacuum source is the intake manifold.

 

On 5/16/2023 at 6:13 AM, datzenmike said:

The idle up solenoid is mounted on the cowl and when on or activated by the air con being turned on passes a vacuum signal to the actuator on the carburetor that holds the throttle from closing to normal idle. There should be two vacuum lines to the solenoid. One back to the intake and the other to the actuator on the carburetor.

 

[Thomas Perkins]

Is this what your missing.https://www.nissanpartsdeal.com/parts/nissan-dash-pot-f1~16182-w8800.html?vin=&make=Nissan&model=720 Pickup&year=1985&submodel=&extra1=&extra2=&filter=(1=K%2fCAB;2=Z24;3=DX;4=F5;5=LONG;6=4WD;7=CAL)

Edited May 17, 2023 by Thomas Perkins

[Thomas Perkins]

Here is one.I have bought from them.They are good.https://www.megazip.net/zapchasti-dlya/nissan/idle-speed-control-fi-pot-16182W8800?q=16182-W8800.Pay with Pay Pal.This site is cool.They have hard to find original Nissan parts.They now have 10 percent off in the next day.

Edited May 17, 2023 by Thomas Perkins