Choke pull off and Fast Idle? Related?

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1966DartConvertible

1966DartConvertible

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Hi

I have read the "choke-adjust" page here and also the Holley 1920 Manual here but still dont quiet understand how they work.

Correct me if im wrong. When i first turn the ignition key to start the engine, the vacuum created in the carb body pulls the choke pull off out. Correct?

What does this do? opens choke butterfly a little? and also pulls the fast idle cam up and set the fast idle screw on one of the fast idle cam steps? then what?

As the engine warms up, the choke pull off slowly releases and the idle speed goes down? But the fast idle cam is "seated" on one of the cam steps how can the speed go down?

Sorry if im confusing you more, im just trying to understand how this thing works as mine is NOT working! (or most probably not adjusted properly).

As you can see from this picture below, the "U" choke pull off link is way too "wide"... will be adjusting that this weekend hence need your help.

P1040713.jpg


PS: Yes Dan I know I should have bought the brand NEW carb of you... wink ;)

Thanks

Syed
 
No.

When you get into the car, and don't touch anything, the carb should be on the NORMAL "curb idle" screw

The properly adjusted choke thermostat is putting spring pressure against the choke linkage

When you floor the throttle, this moves the throttle away from the fast idle cam and allows free movement. The spring tension of the choke thermostat then "sets" the choke butterfly CLOSED as well as "springs" the fast idle cam into place.

When you release your foot, the throttle then stops down with the fast idle screw stopping on the fast idle cam. Again, the choke at this point is normally ALL the way shut.

When the engine fires, the engine would choke itself to death if the pull off was not there. The manifold vacuum seats the pulloff, which opens the choke butterfly a small (specified, adjustable) amount. This then opens the choke butterfly enough that the engine will run without excessive choking,

and of course, as the choke thermostat warms, it slowly opens the choke more and more, as well as dropping down the fast idle cam. The choke normally opens, and the fast idle cam drops due to gravity.

The pulloff does not affect this because it uses a slot somewhere in the linkage. You must realize, that the pulloff OPENS the choke a tiny bit from CLOSED, but because of the slotted linkage, does NOT RESTRICT further opening.

You can see this happening yourself.

With the engine stone cold, remove the filter so you can see. Carefully watch the linkage, the fast idle cam and ONE time open the throttle wide and let it go back. You will now see that the choke is closed, and the fast idle set.

Start the engine, and you will notice the pulloff pull in, and the butterfly pull open a small amount.

To simulate the choke warming, you can gently pull down on the thermostat link, and bump the throttle just a tiny bit. The fast idle cam should fall down as you hold the link down a little, and bump the throttle.
 
67Dart273 said:
The properly adjusted choke thermostat is putting spring pressure against the choke linkage

When you floor the throttle, this moves the throttle away from the fast idle cam and allows free movement. The spring tension of the choke thermostat then "sets" the choke butterfly CLOSED as well as "springs" the fast idle cam into place.
Click to expand...

I guess my problem is... as you can see from the picture, the choke thermostat is not hooked up (that is becoz I dont have one). I would need to get one of this http://www.ebay.com/itm/CHOKE-THERM...Parts_Accessories&vxp=mtr&hash=item4843ad2f78 or the electric choke, for the cold start system to work, right?
 
In a word, yes, you need a choke thermostat. I'm no expert on /6's do you have the proper intake manifold?

You have a shop manual?
 
67Dart273 said:
In a word, yes, you need a choke thermostat. I'm no expert on /6's do you have the proper intake manifold?

You have a shop manual?
Click to expand...

Yes, on both counts.

P1040707.jpg


Thanks for your thorough explanation. At least I now have an idea how the choke system works.
 
Yep, that's what's missing and needed to make things work.
 
67Dart273 said:
No.

When you get into the car, and don't touch anything, the carb should be on the NORMAL "curb idle" screw

The properly adjusted choke thermostat is putting spring pressure against the choke linkage

When you floor the throttle, this moves the throttle away from the fast idle cam and allows free movement. The spring tension of the choke thermostat then "sets" the choke butterfly CLOSED as well as "springs" the fast idle cam into place.

When you release your foot, the throttle then stops down with the fast idle screw stopping on the fast idle cam. Again, the choke at this point is normally ALL the way shut.

When the engine fires, the engine would choke itself to death if the pull off was not there. The manifold vacuum seats the pulloff, which opens the choke butterfly a small (specified, adjustable) amount. This then opens the choke butterfly enough that the engine will run without excessive choking,

and of course, as the choke thermostat warms, it slowly opens the choke more and more, as well as dropping down the fast idle cam. The choke normally opens, and the fast idle cam drops due to gravity.

The pulloff does not affect this because it uses a slot somewhere in the linkage. You must realize, that the pulloff OPENS the choke a tiny bit from CLOSED, but because of the slotted linkage, does NOT RESTRICT further opening.

You can see this happening yourself.

With the engine stone cold, remove the filter so you can see. Carefully watch the linkage, the fast idle cam and ONE time open the throttle wide and let it go back. You will now see that the choke is closed, and the fast idle set.

Start the engine, and you will notice the pulloff pull in, and the butterfly pull open a small amount.

To simulate the choke warming, you can gently pull down on the thermostat link, and bump the throttle just a tiny bit. The fast idle cam should fall down as you hold the link down a little, and bump the throttle.
Click to expand...
X2. I would just add that the link connecting the choke pull-off diaphram and the choke shaft is adjustable by bending the link. You'll have to look up your specific carb number to get the exact setting but a 1/4" pull-off opening of the choke plate is a good start. Make sure the pull-off diaphram is good by applying vacuum to the hose nipple and see if it will hold without leaking down. It's common for them to fail and not pull the choke open causing flooding and real rich running when the engine is cold. Where you are, it's not likely you'll need much in the way of a choke. You can play with the adjustment to get it just right for your needs.
 
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