Here's a breakdown of what you *can* adjust and how, but proceed with caution: incorrect adjustments can damage your engine. If you're not comfortable working on carburetors, take it to a professional.
1. Idle Mixture Screws:
* Location: These are usually small screws located on the carburetor's body, often near the base, one for each barrel (two-barrel carb = two screws, four-barrel = four screws, though some might be linked). They control the amount of fuel entering the engine at idle.
* Adjustment: These are *extremely* sensitive. Small adjustments make a big difference.
* Start with the engine warmed up and running at a smooth idle.
* Locate the screws and very carefully turn them, usually with a small flathead screwdriver. A tiny fraction of a turn (1/8th turn or less) is usually all that's needed.
* Turn them in (clockwise) to lean the mixture (less fuel), and out (counter-clockwise) to enrich the mixture (more fuel).
* Listen for changes in the engine's idle quality. A smooth, consistent idle is the goal. A lean mixture may cause a higher idle speed, while a rich mixture may cause a rough idle or stalling.
* There's no magic number of turns. You have to listen to the engine and adjust until it runs smoothly. Some people use a vacuum gauge for more precise adjustment.
2. Throttle Linkage:
* Location: The linkage connects the throttle pedal to the carburetor's throttle plate. Adjusting it affects the idle speed.
* Adjustment:
* Usually there's a screw or adjustment on the linkage itself.
* Turning the screw can slightly increase or decrease the idle speed. Again, only small adjustments are needed.
* Refer to your vehicle's repair manual for the proper idle speed RPM.
Important Considerations:
* Vacuum Leaks: Before adjusting anything, make sure there are no vacuum leaks in the intake system. Leaks can significantly affect idle quality and make adjustments difficult.
* Repair Manual: A factory service manual for your specific 1983 Chevy 305 is invaluable. It will show you the exact location of the screws and provide the correct idle speed.
* Safety: Always disconnect the negative battery terminal before working on the carburetor to prevent electrical shorts.
Again, if you're not comfortable working on carburetors, seek professional help. Improper adjustments can lead to engine damage.
