Engine Idle issue

[BigOrsnge]

73, 302- standard 2brl carb. Engine fires right up and idles a little high but when I hit the gas pedal to idle down (after engine is warm), it doesn’t idle down. It does idle down when put in gear, but whiplash isn’t fun. Idles fine in gear and runs fine. Choke issue? I’m no mechanic...just looking for ideas.

 

[jagbucket]

sounds like you have an automatic choke if so and all parts are working freely these are on the right side of the carb . See if the fast idle screw is still engaged when hot ,right side btm of carb middle. If so try adjusting the black canister to the lean side small amounts mark the present position and turn one or two notches lean and try a cold start again . to turn the canister loosen the three screws enough to rotate the cap, ir will be marked for lean and rich.
The idle adjustment screw is on the driver side the adjustment screw on the passenger side is for fast idle during choke only.
If the choke is working normally look for a vacuum leak

 

[jckkys]

In short yes it's a choke issue. The automatic choke has a piston in the choke housing that gets stuck in it's bore. Cleaning isn't easy but is worth it. Vacuum in the bore is fighting the thermostat bi-metal spring. You can turn the thermostat to lean, but the choke will not work correctly if the pull off piston is sticking in it's bore.

 

[blubuckaroo]

Not necessarily a choke issue.
Maybe the idle is just set too fast or the throttle linkage is binding.

 

[DirtDonk]

All easy things to check. Another common issue (still with the choke) is that the fast-idle cam simply gets stuck in a higher position. Once the heat releases the mechanism's tension, the cam comes down by gravity only (at least on some carbs) and if it's a little sticky might not release fully.

My first go-to thing is a nice cleaning with carb cleaner, then a quick lube with something light like WD40. It's not a permanent cure, and you don't necessarily want to use a real sticky lube like LPS or something that's going to eventually gum up the works. But it's a good quick test to see if anything is sticking.

If that doesn't work, then you can dig into the mechanical aspects and adjustments.
How high does it idle right off the bat?
Have you removed the air cleaner housing to see what's going on at the carb? If so, how long before you can see the choke open up?
You should be able to watch it open over the first few minutes, and see the fast-idle linkages do their thing.

Paul

 

[BigOrsnge]

Thanks! It a year old carb, and like how it’s running minus the inability to get the idle down after warm up.

 

[jckkys]

Have you looked at the fast idle cam to see if the arm on the throttle shaft is on the cam after warm up? There is an arm on the back of the choke housing that extends forward. Push it down when the idle is too fast. This will override the normal fast idle mechanism by turning the fast idle cam away from the screw on the pass side end of the throttle shaft. The throttle will then close to the curb idle screw, if nothing else is holding the throttle open. If this problem just reared it's head and hasn't existed before, The choke's fast idle cam is the most likely cause. Automatic chokes often get gummed up if not kept clean.