fluctuating idle question 81 720

[sidewayzvegan]

Hey guys,  I have a question that I am hoping someone can help with.  So my 1981 720 2.2 runs good, but I have had some issues regarding the idle.  It seems to idle high, around 1500 most of the time, but it has shot up to around 3000 occasionally, and to top it off, very rarely it will go on down to around 800.  I dont know wtf.  I have checked the vaccuum system and its great/ no leaks. The thing is reading great on the smog machine, but it wont pass because of the idle.  I am going to reground the whole thing, but I still think it may be something else and I would love some input.  I would just tune it down to pass smog, but that is not solving whatever the issue really is.  I have a feeling its electrical.  Any ideas?

 

thanks

[datzenmike]

Hope this isn't a California vehicle.

 

 

1/ Check the choke plate is fully open when warmed up.

 

2/ Check that the fast idle cam has lifted up out of the way of the closing throttle. It should be lifted by the choke as it opens fully.

 

This is the fast idle cam, the ivory colored plastic thing with the steps on it. Right now it is engaged and the throttle is closed on one of the steps (second highest) holding it open.

 

 

As the choke warms a linkage lifts the cam up and the throttle closes on less and less until when fully warmed up it is idling normally. The fast idle is set at the factory and does not need adjusting.... it just needs to be clean and loose. Spray liberally with WD-40 and work the moving parts back and forth to loosen them.

 

 

3/ This could be a badly adjusted BCCD. It the round thing on the valve cover side of the carb. It's senses high vacuum when decelerating and opens and lets in extra air and gas to reduce emissions. If set too sensitive it will activate and often not shut off when you get down to idle. To decrease the setting point sensitivity turn the screw in the middle counter clockwise in half turn increments until idle drops.  

 

It's this round thing. Has a small adjusting screw in the middle under a rubber plug.

 

 

4/ Check that the throttle cable is not too tight.

 

5/ Check the primary throttle shaft is not worn oval. This will allow the throttle plate to move to the side and rub the side of the barrel and catch there rather than closing properly.

 

6/ Check the secondary barrel with a flashlight. It should be fully and completely closed.