80' 720 carb Woes

[ZombieKthulu]

So I am a dumb broke college student and I bought my 80 720 4x4 thinking it wouldn't take much to get it running. All it needs is a new muffler and the Carb rebuilt! Or so I thought.

 

4 months later I got a remanifactured Carb and I can't get the thing dialed down. For whatever reason (pretty sure its the choke) the cold idle is at 3500+ rpm! I have tried messing with the idle screws, adjusting the choke housing, and it still wont calm down. It might be the choke pull off but I'm not even sure. I don't know enough. A mechanic told me to get rid of the whole truck but I do like it. Its my first truck and I love Nissan. Can anyone help? I'm at wit's end!!!

[datzenmike]

Look down the secondary barrel. (the one closest to the valve cover) It must be shut tight. If you find it open a crack try pushing down on it with a stick to close.

[ZombieKthulu]

Nothing is frozen on this Carb. The choke plate moves freely and even opens up after it heats up. Yet the crazy high idle doesn't change.

[ZombieKthulu]

Also when I turn it off it'll chug a few times before it stops running. I'm so worried that I'm gonna have to junk this thing.

[Dat Lurka]

Calm your shit bro. Check the throttle linkage, try turning it by hand to see if it brings the idle down. Maybe put a return spring on it.

Then theres the idle cam, if it's catching on the highest part then idles gonna be way up. I had mine wrong and had to take the carb off and redo all the linkages.

[datzenmike]

Did you....

 

Look down the secondary barrel. (the one closest to the valve cover) It must be shut tight. If you find it open a crack try pushing down on it with a stick to close.

 

 

 

 

Nothing is frozen on this Carb. The choke plate moves freely and even opens up after it heats up. Yet the crazy high idle doesn't change.

 

This is not the same thing. The secondary is the other barrel. Use a flash light and look down it and be sure it's fully closed. Only has to be open a crack to give fast idle.

 

 

 

 

 

Then theres the idle cam, if it's catching on the highest part then idles gonna be way up. I had mine wrong and had to take the carb off and redo all the linkages.

 

This is also a possibility, but I wanted to be sure the secondary wasn't stuck open first.

 

This is the fast idle cam... see the underside has steps???

 

 

When the choke is on, the cam is pulled into position and the throttle closes on one of the higher steps and is held open. Below you can see a set screw is on the second step and is holding the throttle open as described.

 

 

 

When the choke warms up the cam is weighted and falls out of the way until the motor cools and the choke is back on again.

.

[80daterpillar]

I'm with mike, pull back the fast idle setting, mine came out of the box the same way...

 

I assume when it warms up it idles down?

[datzenmike]

When the choke is on there is a linkage that does down and lifts up on one side of the cam rotating it. The throttle will close on one of the steps. When warmed up the linkage moves away and when the throttle is lifted off the step the cam is free to drop back down by it's own weight. That's why there is more plastic on one side to weight it.

[ZombieKthulu]

OK this is just what I was looking for I think. I'll certainly let you all know if it helps. I really do appreciate it. I've been so stressed out about this but I do need to calm down and get it figured out.

[wayno]

I would also check the PCV valve, if it is open, the idle goes crazy.

[ZombieKthulu]

Datzenmike thank you so much. I did exactly what you said and the idle dropped way down. Running at a pretty 750 rpm. It after it warmed up it went up to 1200 for a bit but went back down. I think that has to do with my lack of a heat riser hose. Seriously relieved though thanks again