Adjust choke

How do you adjust the choke on a 1984 GMC pickup. 305 engine. In the winter the choke sticks and the engine runs away with you and I can’t get it to idle back down.

The first thing to try is cleaning up all the linkage to the choke and the high idle cam. You can do that with spray carb cleaner. Do not use anything that leaves a residue of any kind, such as WD40.

If it’s still sticking, try replacing the bimetallic spring that operates the whole mechanism.

If that too fails, the problem may be wear. The shafts on the choke plate can wear grooves in them where they go through the carb body, causing sticking. Try checking the choke by moving it around by hand to see if there’s any looseness.

Post back with the results.

The heat riser is not working properly to divert a small amount of hot exhaust gas to the choke coil, most likely. Or the choke coil is sticking. Spray it with carb cleaner. You may have to replace the riser or the coil. This is not rocket science and if you have a general repair manual it will make it seem like childs play.

You may need a new choke thermostat, which may be electric. If you’re lucky, this may be the easiest job of your life.

As soon as the engine starts, some sort of a vacuum device, a dashpot mounted on the side of the carb or an internal piston should pull the choke about 1/3 of the way open and allow a fast idle cam to change positions and lower the idle speed.

In 1984, they used sealed “smog carburetors”. The choke thermostat was held in place by pop rivets, not screws, to prevent “tampering”…The rivets can be drilled out and replaced with screws if adjustment or replacement is required. I suspect by now your carb has been replaced with an “open” carb off an earlier model or has been “de-smogged” so it can be adjusted.

Hold the throttle open a little (engine off) and close the choke with your finger. You will see the choke fast idle cam move up and hold the throttle open more then normal. You can adjust the choke fast idle speed with the screw that rests on that plastic cam…As the choke opens, the cam drops and idle speed returns to normal…

I hope this description helps you…