Adjusting the Choke on a SL6

Getting the choke to work well can be a challenge.

Here are some simple steps to adjust the choke on a SL6

First you must be sure the choke "stove" is working correctly.
The choke "stove" (well) is the housing and rod unit bolted to the exhaust manifold. It provides the spring tension to close the choke flap.
Check it's operation by removing the air cleaner and working the throttle, the choke flap should be pushed completely shut with light force.
If the choke does not close all the way or if the choke flap shuts real hard and stays on to long, unbolt the stove unit from the manifold and adjust it's spring tension. The choke flap needs to close fully with light force when cold. This adjustment must be done first. (More well choke info.)

You will notice that when the flap shuts, a linkage rod pulls the "staircase cam" onto a fast idle setting. With the choke flap fully closed the choke's fast idle adjusting screw should be on the highest cam step. The position of the fast idle cam can be adjusted by bending the "L" shaped rod leading down to the cam.

The next step is to start the car and watch as the vacuum pod pulls the choke flap open. This should allow the cam to drop down to a lower step and reduce the fast idle speed a bit. If this does not happen then check to see if the vacuum pod is bad or of the linkage is binding. During the first few moments of starting the car, try opening or closing the flap a small amount by hand to see if the engine runs better. If it does, you need to adjust the "U" shaped "operating link" shown above. (large arrow) Opening the "U" wider will keep the choke closed and up on the higher steps of the fast idle cam. Squeezing the "U" shut will open the flap more and drop the fast idle cam to a lower step / slower idle speed. This is a key adjustment and bending the choke's operating link a small amount has a major effect on over-all choke performance. The factory used a micrometer to make this adjustment!


Finding a nice choke setting is a "trial & error" process and you only have a few minutes to work on adjustments before the car will warm-up enough to kick the choke off. It is best to do some fast checks then shutoff the car and make your adjustment(s). It is not unusual to have to "tweak" then drive the car a day or two, then tweak again. In some cases, the fast idle cam steps may need to be filed down so the drops in mid idle speeds are not as great. (The tall step can be shortened so the drop to mid speed is not as big)

Most people (and modern day mechanics) don't like the idea of bending rods and filing parts to adjust a choke but that is how it's done. When you have it correct, you can hop in your SL6 car, pump the gas to "set" (close) the choke, start the car and it will run on a comfortable fast idle, tap the gas and it will "step-down" to a reasonable mid-speed idle so you can stick it in gear without a "bang" or a stall-out. After a few minutes of driving, the choke comes off completely and you have "curb idle".

In General, if the engine starts and runs a moment, then stalls, the operating link "U" should be spred open more.
If the engines starts and runs OK for a moment but then gets rough, "chugs", puts-out black smoke then stalls, the U needs to be squeezed shut some or the vacuum pod is blown and not working.
If the car starts runs but then stalls when going to mid idle, the cam has to big of steps or the link is mis-adjusted.

Here are other parts which should be checked to be sure you get good cold engine operation:

-Distributor Vacuum advance and mechanical advance must work.
-Valve lash adjusted correctly.
-No Intake vacuum leak(s) or overly lean main jet in the carb.
-Accelerator pump works well.
-Clean air filter.
-Heat riser or intake manifold heat to prevent carb. icing. (in cold weather areas)

Here are links to a trouble-shooting guide to help pin-point carb. & choke problems:
Troubleshoot page1 - Troubleshoot page 2 - Troubleshoot page 3 - Troubleshoot page 4

So get out there and give it a shot, the choke and carborator adjustments are not that complicated once you work with them a bit.

For general carb. operation information, these links on the Holley 2280 give a good discription on the different systems.
Special Thanks to Julie Roth for providing many of the following specs.
Holley 2280 page1 - Holley 2280 page 2 - Holley 2280 page 3 - Holley 2280 page 4
Holley 1945 page1 - Holley 1945 page 2 - Holley 1945 adjustment specs.

Carter BBS (1 bbl) - Carter BBS pg. 2 - Carter BBD (2 bbl)
Smog machine instruction manual and carb. adjustment information. (PDF file type)