Hard to come out of high idle

[76GreenBeast]

76 K10 350 w/ 4bbl Q-jet.  Recently I've had to really romp on it to get it to come down out of fast idle in the mornings.  I used to just lightly burp the throttle and it would come down.  I sprayed some carb cleaner on the linkage area of the carb and it did nothing.  The carb "loads up" at idle when the engine is cold (been doing it for 15 years), and I usually kick the throttle a few times (more during winter) to get it into high idle.  Questions:

What's sticking on the carb to cause this problem?
What's "loading up" mean (I've heard people use this term, but never fully understood what's happening)?

Thanks.

[VileZambonie]

check the choke break. do you have one or two on yours.

[76GreenBeast]

I think I have one vacuum diaphragm on the carb, if that's what you're referring to.  How would one check it?  I think my carb is a 4MV if I remember my Haynes manual correctly.

Thanks again...

[VileZambonie]

when you start it up do you see the diapragm react? Is the linkage moving?

[76GreenBeast]

I didn't get time to look at it this past weekend.  I'll probably look at it this weekend. 

For my enlightenment, what does the vacuum pull-off do with respect to taking the truck out of high idle?

Some more info:  The truck does not immediately come into high idle when I start it cold (never has).  The RPM's will increase slightly, then it will go into a loping low idle with a really rich smelling exhaust (some black smoke too).  I have to rev it a few times (more in cold weather), to get it to come up to high idle.  Once it is there, and it warms up (temp needle between the C and the first notch on the gauge), I used to just burp the throttle and it comes down to its warmed up idle.  Once that happens the truck drives grrrreat.

Could a vacuum pull off have been my problem lo these many years?  The carb has been "re-built" twice but I don't know what was replaced/reused.

I hope you guys can help me because they're really isn't anyone around here that messes with carbs anymore.

[DnStClr]

Maybe I can help a little bit- I speak "dummy" pretty fluently. ( No, 76GreenBeast, I'm not callin YOU dummy, please don't misinterpret my speech patterns the wrong way)
 Your carburetor needs a rich mixture of fuel and air when it's cold. So, the choke closes off the choke plate (throttle plate) at start-up. It's shutting down the air supply so the engine gets more fuel to start. By doing so, it also creates a low pressure at the throat of the carb, so extra fuel is pulled into the
circuits of the carb.
As soon as the engine begins to idle, the rich fuel/air mixture needs to lean out to prevent stalling, so the choke pull-off, (or choke break, as VileZambonie calls it, or vacuum break, as it's also called,) has to react to the change iin engine vacuum in the manifold. So it slowly begins to allow the throttle plate to open and let more air come into the carburetor. As temp rises, the choke pull-off reacts more, and the throttle plate opens even farther. Soon (like less than a minute) the engine is idling slower because the choke pull-off has allowed the throttle plate to open fully. The carb venturi is creating enough vacuum to pull the right amount of air in to mix with the fuel, and your ready to rip.
 Now you know why VileZambonie asks you if the Diaphram is reacting in the choke pull-off. If it's got a bad diaphram, your carb will not transition from high to low idle very well on it 's own. It might not even go into a high idle mode.
   Hope this helps a little.

[76GreenBeast]

Thanks for the info.  So once the engine is started, how long should it take for the engine to go into high idle?  I have to rev it up to get it into high idle (multiple times) so it will stop belching rich exhaust.  I then usually burp the throttle once its warm to bring it down.  It will come down on its own but I usually don't let it idle that long. 

Thanks again. 

[DnStClr]

Should go into high idle immediately when you start the engine. As the engine starts to warm up, the temp causes a bimetallic spring attached to the choke to react to the increase in temp. That's when the linkage on the choke moves to open the throttle plate and allow more air into the carb, and slow down the engine rpms.
An electric choke causes the spring to move using a little heating element inside the choke housing.
 

[76GreenBeast]

So all signs seem to be pointing to a bad or malfunctioning choke pull off.  I'll try to check it out tonight when I get off work.

I think the loping/rich exhaust condition and this recent inability to come out of high idle issue are related.  Now, when I start it and drive it when the engine is still cold I have no problems (its a little stiff but it will run if you're gentle).  This problem occurs when I warm it up in the mornings before I leave for work (my road is heavily traveled so I need all the help I can get getting out of my driveway).

Does anyone know what the proper "gaps" should be for the throttle plate with the choke engaged and with the pulloff fully engaged (and how to measure them)?

This is good stuff, thanks again...

[DnStClr]

Vile had written a previous post on choke adjustment- you have to physically move the choke housing, so you loosen the 3 bolts or drill out the 3 rivets to move the housing. Engine off, of course. when you rotate the housing, you'r increasing tension on the bimetallic spring.Rotating one way makes the choke close at a higher temperature, and rotating the other way makes it close at a lower temp. There's notches on the housing, and a Haynes manual or factory manual tells you what the adjustment should be.
It sounds like your choke is working, but the rate of choke movement is what the choke pull-off controls, and that could be what's going on- 
on edit,Vacuum leaks can also be your culprit.

[76GreenBeast]

Alright.  I just got back from checking things out, and the truck started and warmed up just like it used to do.   I did see the linkage move (or rather I saw that the choke plate was open slightly after it started, I didn't have an assistant start the truck).  The plate did close pretty tight after I set the choke (gas pedal to the floor, and up).  The truck came up to high idle on its own and I literally just brushed my foot across the gas pedal and it came out of high idle.

So I'm thinking....can outside temperature affect how these series of linkages move?  The truck always runs pretty good when its warmer outside.  I did spray some carb cleaner around the choke pulloff/high idle cam area on the carb before I started it, so maybe it unstuck something.  Any explanations???

Thanks so much for the help

[DnStClr]

Sure. It's entirely possible that the carb cleaner helped loosen up the throttle plate shaft so the air could push it open and lean out the mixture.
wow. Can a change in weather temp change the operation of the carburetor/  No doubt about it, but I think  basically the carb is looking for that 'stoiometric" air/fuel  relationship of 14:1 so it can send the combustion chamber the right mix .
just my .02