Holley Carb Choke Operation

[The73vetteman]

I have a '73 with the original 350 motor, but an Edelbrock manifold and Holley 600 installed by a previous owner. I don't think the choke is operating correctly. I can set it by turning the adjustment block on the side, but the actual choke never seems to move, regardless of how warm the engine is.

By-the-way, I disconnected the electric choke, because that didn't seem to do anything either.

Could anyone give me some information on how the choke should work, and any tips on how to set it correctly?

Thanks in advance,

'73vetteman

 

[JohnZ]

The choke isn't operating correctly because you've disconnected it; it needs a full ignition-switched 12 volts (not the reduced 7-8 volts from the coil + terminal) and a good ground to operate properly. The choke plate is closed with the ignition off, and when you start the engine, the bi-metallic coil inside the housing heats up gradually and opens the choke plate to fully open (off). The rate at which this occurs is adjusted by turning the black housing cover in small increments. If you disconnect the power or ground lead from the choke housing, the choke will stay at fully closed (on) unless you really rotate the housing WAY out of its normal adjustment range.

Wire it back up again and start with the housing set to the center of the index marks, and adjust one mark at a time - toward "Rich" for longer choke time, toward "Lean" for less.

 

[brusso]

Also, if you have a volt meter, with the engine running check the wire going to the choke for 12 volts. You should only have 12 volts present when the engine is running, not just the key to the on position. This is to keep the choke from "warming up" if the engine stalls. A relatively simple circuit to troubleshoot. If you have 12 volts and no choke operation then it could be a poorly grounded choke or broken choke spring.

 

[tazdevl35]

If I'm not mistaken the choke coil feed comes from the alternator terminal that is hot only in run (brown wire if i remember correctly) and as stated above it keeps the choke from opening when the engines in in key on engine off mode.As far as the setting goes, the way I do it is to let the car set overnight , loosen the choke plate adjuster screws(3 of them) and turn the plate with a screw driver till the choke plate is just touching the all the way closed position. Also the fast idle cam screw must be set as well to ensure the throttle plate is open enought to keep the enging from "loading up" while the choke is on. I like to set mine at around 2100 on full choke cold start and it rises from there. Then you can kick it down as the choke opens and the idle increases. BTW ,if you use a factory air cleaner with choke stove, be sure the preheat tube is intact and the door closes to let the warm air in on start up and while cold. This will eliminate cold tip in stumble till the motor is up to operating temp. Sometimes it stays closed all the time but only on the coldest days to let warmer air be fed to the carb to prevent stumble. The temp "switch " for the thermac door is in the air cleaner and has 2 vacuum hoses attatched to it. If it goes bad and doesnt work at all it is replaceable. I belive it is still available from GM.



Later,


Taz

 

[The73vetteman]

Thanks for all your replies. I understand what you mean about the electric choke, but I think my problem might go a bit deeper.

When I take off the electric part (basically a bimetallic coil that I assume serves to open the choke as it warms up) underneath that, in the metal housing, is a lever and piston assembly. There was also a fair bit a black crumbly debris, and the piston moves very freely.

My guess is that there is supposed to be a seal around the piston, and that it moves as the air behind it warms up. Or is it some kind of damper?

73

 

[motorman]

the little piston is the "choke pull off" the part that opens the choke part way as soon as the engine starts. as the spring heats up and looses it tension the piston will pull it all the way open. the spring action also helps open the choke