I have an 81 300 with the stock carter 1bbl. My idle is extremely low, so low I can barely hear the truck running. How can I adjust my idle? Ive tried search and my manual but cannot find the idle screw anywhere! Also, I seem to be running a bit rich, and I cant find a way to adjust my fuel mixture. I tried searching and came up with nothing. Any help is greatly appreciated!

 

The idle speed control screw is on the driver side toward the front, the screw end butts up against the carb body. There's probably a reason it's idling low. Make sure the carb is bolted down tight.

 

I agree, make sure all the bolts are tight first off. Then, where the throttle cable comes in in the back of the carb, there are two screws (about an inch apart), on the driver's side in the back. You will probably have to remove the air cleaner to get to them, and they're kind of a pain to access, simply because they're back by the fire wall. IIRC, the upper one controls the normal idle, and the lower one controls the idle when the engine is warming up. You can tell because the normal idle screw rests against the body of the carb, and the warm up screw rests against a rotating arm that's integrated into the choke. Rotating the screws one way or another will raise/lower your idle.

The idle mixture screw (which adjusts rich/lean) is located on the passenger side of the carb's throttle plate (at the bottom), towards the front and is much more out in the open.

 

I tightened down the carb and no change....I also tried looking for both screws, there are two on the drivers side near the rear of the carb, I tried turning them both ways and no change....anybody have a picture I could take a look at?

 

Those are the two screws. Their operation is extremely simple. If you turn them in, they'll physically push against the body of the carb and push the throttle outwards, which simulates you pushing on the gas. If there wasn't any change, they very well could be turned out so far that they're not touching the carb.

The way to tell them apart is one of them will push against the actual body of the carb (that's your normal idle), and the other will only push against an arm attached to the choke with the engine is ice cold (that's your high speed to warm the engine up when it's cold). The screws are off-set from each other and the high speed idle is the one closest to the firewall.

Let the engine completely warm up and then remove the air cleaner. Look at the choke plate on top and make sure the plate is completely straight up and down. If it isn't, loosen the three screws that hold the choke in place and rotate it gently just until the plate is completely open and stop and tighten down the three screws. Now let the engine completely cool and look to see that your choke plate is open about 1/8" - 1/16" or so. If it's completely closed, you'll want to readjust until it's open a tiny bit, or it'll never start.
This makes sure the choke is set (before everything else).

Now that the engine is cool and the choke is set, start the engine and adjust the high speed idle screw (the one closest to the firewall) until the engine idles at 1200 RPMs. When you turn it inwards, it'll begin pushing on a rotating plate that has a series of steps on it. The further in you turn it, the more it will physically push the throttle out. The only reason it shouldn't do anything is if it is not actually making physical contact.

After it's set at 1200 RPMs, let the engine warm up completely and then throttle the carb. It should kick off the high speed idle (that stepped plate will turn and the high speed screw will no longer be resting against it). Now, rotate the normal speed screw inwards until it makes physical contact with the body of the carb. Continue to turn it in until it pushes the throttle plate out far enough to bring the idle up to around 600 or 700 or so.

The idle speed screws are 100% physical. There's no vacuum or any other types of mechanisms involved. They basically simulate your foot pulling on the accelerator cable to bring the RPMs up by physically moving the throttle.

Let me know if that helps.