High idle until I rev the engine...

[RudeDog]

I have a '78 (stock equipment) and have a problem with the idle speed. While driving, if I come to a stop the idle speed is high (tach is not working or I'd give numbers). If I then give the engine a slight quick rev and let off the gas quickly, then the idle speed ends up reduced to a more normal idle speed. It is very consistent. Any thoughts?

Rudy

[So Cal Mark]

throttle plate sticking

[majicwrench]

Or choke not quite all the way open. Choke plate should be straight up when engine hot, or it will slightly engage the fast idle cam.

[RudeDog]

Alright, I spent all day doing a carb clean and rebuild and I think I figured out the problem. I'm missing a part but I don't know what to call it or whether I can replace it or not. Here's the deal:

There are 2 levers on the side of the carb that work with connecting the air pollution vaccuum device to the primary throttle. One of the levers connects the rod coming from the diaphram of the vaccuum device with another lever that controls the throttle. The other lever is on the same shaft as this first lever but it has a removable rod attached to it that goes up into a small hole between the vaccuum device and the main body of the carb. I believe this is called the bowl vent valve area but I'm not sure. Anyway, it looks like there is supposed to be something inside the small chamber that the rod goes into that gives downward pressure on this rod thus allowing the throttle to completely close. I don't have anything in this small chamber and I don't know what is supposed to be in there... it's just a small rod going into a small empty chamber. There is a small metal piece that is pressed into the carb body at the top of this little chamber that holds a small rubber valve in place within the carb body but otherwise there is nothing in this little chamber. What part am I missing? For now I used a piece of string to pull the lever down thus allowing the throttle to completely close at idle.

Thanks,
Rudy

[ga.spyder]

Hey Rudy any chance you could post a picture.I bet someone could answer it right away for you.
Craig

[RudeDog]

Yeah, I guess I had to figure out how to post pictures at some point...



You can see the rod that goes up into a small hole on the underneath side of the top part of the carb. It attaches to a lever that is behind the visible lever with the string wrapped underneath it. The string is providing downward pressure (pulling the rod out of the small hole) which keeps it away from the lever that allows the throttle plate to go closed all the way.

The part that I think I'm missing is the part that goes in the small chamber that the rod goes up into. I think it is some sort of spring loaded contraption that keeps the rod pushed out of the hole as far as it will go except when it is activated (by pressure I'm guessing). I'd take a picture of the chamber but I'd have to remove the top part of the carbuerator to do so and I don't have time right now. However, the chamber I'm talking about (the one that the rod goes up into) is right next to the float chamber. It's shaped like a small cylinder (smaller in diameter than a dime) with a pressed in metal piece at the top which holds a rubber valve in place within the top portion of the carb. I think the part I'm missing is supposed to attach to the metal piece that is pressed into the body of the upper carb and probably has a spring of some sort that pushes downward against the top of the rod that is going up into the small hole (visible in the picture).

Does that help? I can hopefully post some pictures of the inside of the chamber that I'm talking about in the next couple days when I have a chance to remove the top part of the carb.

Rudy

[ga.spyder]

Rudy, I think there is a spring loaded diaphram that goes in there. I am not a carb expert,but someone here will chime in with the actual name of that part.I will try to find and send you a link to an exploded view of the ADFA.
Craig
http://files.meetup.com/533614/Artigue_FIAT_124_MM.pdf
All the carbs are covered here.There is great info in this link!