How to Adjust a Carburetor Mix

A carburetor works via suction power generated by the engine to which it is attached. As the suction pulls air in, the carburetor mixes fuel with it to help the combustion process in the engine. Adjusting the mixture on the carburetor affects how much fuel or air the carburetor will allow through the engine intake. The process is two-fold; you can make minor adjustments with simple external screws, and or you can make big adjustments that require accessing the carburetor's jet assemblies.

Instructions

Minor Adjustments

1

Lift the car hood and prop it up. Locate the carburetor. Examine the outside of the unit until you find the air/fuel mixture needle and the idle screw on the carburetor surface.

2

Turn the car on and let it warm up. Insert a screwdriver into the idle screw. Turn it slightly and listen to the engine idle speed change. Turn it outward to increase the combustion speed, or turn it inward to decrease the engine tick-over. Set the needle screw where the engine idles consistently without hiccups or racing.

3

Refer to your car manual for the correct setting of your air/fuel mixture needle, usually specified in a number of turns. Insert the screwdriver into the air/fuel mixture needle and turn it inward until it stops. Remember how many turns you made. Now reverse turn outward the number of turns per the car manual. Turn back inward for more fuel intake and outward for more air intake. Do not go with too much air or the car will overheat and burn the spark plugs.

Major Adjustment

4

Pull the ignition wires off the engine spark plug and use a socket wrench to remove it. Examine the color on the tip of the plug. Note whether the plug is whitish (not enough fuel) or oily black (too much fuel).

5

Locate the carburetor. Disconnect the throttle cable. Loosen and disconnect the securing nuts using your socket wrench and crescent wrenches. Remove the carburetor after disconnecting the fuel line as well with a crescent wrench or screwdriver.

6

Relocate the carburetor to a work bench. Remove the float bowl on the bottom of the carburetor with a crescent wrench. Remove the main jet assembly inside using a screwdriver. Note the number on the jet. Based on the spark plug color, either increase the jet size (more fuel) or decrease it (less fuel). Re-install the jet assembly, close up the float bowl again with the wrench, and re-attach the carburetor to the engine.

7

Re-connect the fuel line and throttle cable. Install new spark plugs and place the ignition caps back on them. Turn on the car engine and let it warm up. Take the car for a ride. After a good drive, park the car and remove the plugs again to check the color. Repeat the jet adjustment process until the spark plug tip is chocolate brown in color for proper mixture in your area and altitude.