Hey guys
I posted this in a differnt section but no one responded. i thought yall might be able to help. I have 77 f150 w/400 C6. I have had this problem acople of time. it seems to happen radomly. When i start the truck and back out of the driveway its fine. but the next time i go to take of the enging practically dies and then it wont idle right. it idles at like 200. If i put the truck in neutral and try to rev it wont go over 2000. I can temporarily fix it by jiggling the throttlle linkage, butterfly vavle, and all the other stuff on the carb in side the enging compartment and then rev it while i am in there. When you do this the RPM come back up and its fine. This is a really irrtitating thing. Any suggestions?
Thanks
David

 

Which carb do you have?

If you can make the problem go away (even temporarily) by jiggling linkages, then that's where you should look first.

I would suspect some linkage is out of adjustment, maybe loose (or faulty) connections between linkage and carb, or maybe linkage that needs lubrication or cleaning to prevent binding.

 

I have the edelbrock 1406. It started oding this after i put the stock air cleaner one to prevent carb freezing that was occuring. I was in there again this morning so i could get to school an ithink the stock air cleaner might have been making the choke stick. I put the open element back on to see if it stops the problem. I'l know wheni leave school today. I will try cleaning the linkage. I do have a spacer ring under tha aircleaner but i donthink it gets it high enough. Could i use two rings one on top of the other?
thanks
David

 

Well i just got home. It did it again when i left school. But no matter how much i messed with the linkage it didnt help. So i tried adjusting the idle mixture. I turnde it just enogh to smooth the idle and it ran fine all the way home. The adjuster screws were in the same place they have been for months. I am utterly confused.
David

 

In the Edelbrock install guide, it says running the stock 10" aircleaner will affect your carb A/F ratio. I'd think that would matter more at WOT than at idle though. But if you had to adjust the idle screws to smooth it out, that could be your problem.

 

I ran the open element for months without trouble. Then this winter i went to the stock cause the carb was freezing. Since i changed to stock i have been having a lack of power cause it cant breath through the stcok one and now this. On the way home from work it ran fine but at the stop light some time it would idle really low like 200-300 RPM but faily smooth and it would take off fine. I am about to sell it and buy a remanufactured one.
Later
David

 

David,

Don’t go wasting money on a different carb just yet. It sounds like the choke is not doing what it is supposed to do. When it idles very low it could well be that the choke plate – the flapper at the top of the carb – is being pulled closed. That will greatly restrict airflow and cause the mixture to go very rich. Both will greatly affect the idle speed. It also sounds like the times that you were able to fix the problem by jiggling the linkage you were in fact making the choke plate open back up.

Therefore, spend some time carefully looking at all the linkage and especially the linkage associated with the choke. There is a fair amount of it on both sides of the carb. Manually open and close the throttle with the air cleaner in place to see if there are ANY places that it does not travel smoothly. Then with the top only off the air cleaner do the same thing. With the throttle partially open and close the choke plate. Are there ANY spots where it does not operate smoothly? Move the throttle to the just barely open position and do it again. What you are trying to do is simulate what happens when you are driving.

One other thing to check are the two metering rods for the primary jets. Have you changed them out? One may not be functioning properly and staying in the up (power mode) position when the throttle is returned to the idle position. This will cause it to run very rich and thus idle slowly.

Spend some time on it and I’m sure you will find where the problem is. Pay attention to how everything works together and you should find where it is malfunctioning.

Good luck,

Mark

 

I am running a Carter AFB and also had to use a spacer under the air cleaner. Don't remember what hit. Anyway if it is a choke problem I would definitely look for bent or bound choke shaft or linkage. Something else to check, my electric choke cover cracked and the choke no longer works right. I readjusted mine to make sure it opens all the way. It doesn't close all the way now but this is SoCal and we don't have winter so I get away with it. Also maybe the air cleaner disturbed the choke pull off adjustment and I would check that.

 

i would think that if it didnt start untill you replaced the air cleaner , the problem is the air cleaner,bob