I have a 1966 corvette Holley 3884505-DA /3367. Can anyone tell me how the choke works? If you have a pic that would be great. I called Holley and they have no info on it, they say it was a GM deal. Thanks

 

There is a thermostatic spring on the intake that when cold it keeps the choke open on the carb. When the engine warms up the spring closes the choke. The adjustment procedure is in your AIM and GM service manual

 

Blackvette

'66 300HP should have intake manifold 3872783; cast iron with a pocket cast on passenger side to house the divorced choke components. Is this how your car is equipped?



The divorced choke consists of bimetal spring #3887148 - it is lightly/faintly stamped '7149' on the outermost coil. The correct choke rod is 3881866, unmarked but ~2.80" c/center (not developed) length. There's a choke cover, Zn or cad plated, attached by small machine screw into manifold.






With a cold engine, the bimetal spring pushes UPWARD, CLOSING the choke plate. With warm engine, the spring, the spring pulls DOWNWARD, opening the choke plate.
* There is NO choke adjustment procedure found in an AIM.
* The choke adjustment procedures found in 1966 ST72 Chassis Service manual are INCORRECT. Here's correct steps, pictured below. You must insure that you have proper bimetal spring coil as Quadrajet & Rochester appear similar, but work in opposite direction. Pay attention to the part numbers & try to find real GM spring. Hope this helps.

 

That's exactly backwards to the way it works.

 

You got some good information from the above posts. Of all the systems on our cars this seems to be one with a large learning car. Once you got it, you got it though. Your right Holley tech department "ain't what it use to be."

I don't worry so much about the exactness of the choke butterfly distance around the primary air horn. If its close its good enough for me. Check the choke pull off works when you get manifold vacuum. (Thats the circular diaphragm in the picture of post 3) If that works the next mystery is how you set the fast idle. From the same picture in post 3 that shows the choke diaphragm, to the left of that is a lever arm with a slot in it. That slot is for a screwdriver that you twist depending on if you want the fast idle faster or slower. when you twist the slot it slightly changes the location on the plastic fast idle cam. This is set when the engine is cold and you push the accelerator to the floor. Once you play around with it, you will get the idea. Problem is you only get to play with it when the engine is cold as once the engine is hot the bi-metal spring springs goes into action and starts working against you. I hope I did not confuse you, but this is my understanding of the system. The service manual instructions are clear as mud until you understand the system, then they make sense. I believe the overhaul manual may go into a little more detail on the choke. Good luck. Mark

PS: Be careful of the fast idle speeds in the service manual. In my opinion they are to high. If I remember correctly the book called for 2200 RPM for my application. I did that once. I set my fast idle at around a comfortable 1500 RPM. Also I think there is a paper on this system that John Z published. Cheers.

 

Thanks for the info. I have an aftermarket intake so this wont work. I will probably change carb. I am not worried about originality. Thanks

 

Consider an electric choke. Check with the manufac. of the carb to see if one is available. Jerry

 

I just want to mention that using the factory method to set the fast idle speed is done on a hot engine. That's why the speed is set at approx 2200 RPM hot. When the engine is cold the speed will be much lower.

 

I just want to mention that using the factory method to set the fast idle speed is done on a hot engine. That's why the speed is set at approx 2200 RPM hot. When the engine is cold the speed will be much lower.

 

Thanks Tbarb, I had no idea, but that makes sense. Mark

 

Actually, it doesn't. The fast idle is higher on a cold engine and drops down as the engine warms up. The choke is ON and the fast idle is HIGHER on a cold engine. As the engine warms and the choke pulls off, the fast idle decreases.

 

Changing the carb to a different style that will accept an electric choke may be your best option.

 

That is to be expected - you are dealing with an almost 60 year old application and YES it was / is a GM deal - although Holley actually did sell choke stats for that application LMAO !

 

AFAIK ( I am pretty certain) there are no electric choke conversions for manifold "crossover" choke applications - usually any electric retrofits are for the hot air type chokes.
You might be able to convert to manual (cable operated) choke - that may require a little effort sourcing an applicable conversion kit.

 

Usually the fast idle speed does not come down until the throttle is tapped or blipped as the fast idle cam remains set in the initial fast position when the choke was first set - the choke may open but usually until you tap the throttle the engine will keep revving

 

if that is a original 3 digit date code carb its a very valuable part

 

When you set the choke fast idle (high step of the cam) on a hot engine the same setting (throttle blade position) on a cold engine will result in a lower RPM because all the fluids are cold.

After start up, the choke pull off opens the choke blade slightly and a tap of the throttle will allow the fast idle to drop to the next lower step. As the blade opens the fast idle keeps dropping accordingly.

 

Whatever - you win !
Now help the guy to make his choke WORK