Carburetor Tuning Tools & Components

Using a carburetor tuning kit will improve both engine horsepower and performance. This includes idle, part throttle, wide-open throttle, cruise, and transitioning between these different stages / circuits. Changing carburetor components that affect fuel flow (such as jets) to match the engine's needs will reduce bogging or flat spots during acceleration.

By investing a small amount on motor carburetor tuning and/or rebuilding, you will save a lot of money instead of purchasing a new carburetor, which may need tuning to optimize performance as well.

There are many different types of carburetors, so consulting the owner's manual / guide for the specific carburetor you are working on is the best option for proper tuning and carburetor adjustment. The two most popular types of performance carburetors are from Holley (including variants from other vendors) and Edelbrock. To prepare for the proper tuning of a carburetor, confirm that the correct fuel pressure is reaching the carburetor with a gauge as well as the correct ignition timing for the engine. Next, with a warmed up engine and a vacuum gauge, record the vacuum reading at your engine's correct idle speed using a port either from the intake manifold or below the throttle blades on the carburetor. Next is idle mixture screw adjustment. On Holley carbs, the screws are located on the metering blocks (on either side of the main body). Typically, there are either two or four screws. When Edelbrock carburetor tuning, these screws are on the front. When adjusting a carburetor idle screw, the goal is to adjust it to the "lean-best" setting. To do this, with the engine warmed up and at idle, and using a vacuum gauge connected to engine vacuum (use a carburetor vacuum fitting below the throttle blades), turn one of the screws clockwise until you get the highest vacuum reading on your gauge. When you reach the highest vacuum reading, turn it counter-clockwise just a slight amount. If turning the screw clockwise does not increase vacuum, turn it counter-clockwise to ensure the screw is not set too far one way. Then, repeat the same process to the other idle mixture screw. Since changing one idle mixture screw affects the other, go back to the previous idle mixture screw and adjust it. Continue this adjustment between the two screws until the highest vacuum reading is achieved for both. Record the engine vacuum reading for the next step. The idle screw adjustment process reduces the amount of unnecessary fuel at idle and prevents spark plug fouling as well as improving engine fuel efficiency. Taking your vacuum reading, confirm that either the step-up springs (in Edelbrock carburetors) or the power valve (in Holley-style carburetors) are properly matched to engine vacuum using a manufacturer manual tuning chart. To do this, take the idle vacuum reading and divide it by two. The result is what you need to match with the power valve or step up springs. If you are between two options, select the higher number. The step-up springs in an Edelbrock carburetor help to pull the tapered metering rods out of the jet holes when there is less vacuum than the spring is rated for, providing metered fuel when the vehicle accelerates. The Holley power valve helps enrich the fuel mixture in a different way, but below its vacuum rating, like the step up springs. More information on proper tuning and operation is available in your carburetor owner's manual. Holley adjustable vacuum secondary carbs also follow a similar procedure for the correct vacuum secondary diaphragm spring and can be changed as necessary. Edelbrock Thunder AVS carburetors use set screws to adjust vacuum secondaries (Edelbrock Performer carbs are not adjustable and have to be modified). Another adjustment for both carburetor versions is the float. On Holley adjustable float carbs, this is adjusted externally by loosening the nut on top of the fuel bowl and turning the screw until fuel just reaches the bottom of the sight plug hole (plug removal required). The nut is then retightened and the sight plug is reinstalled. This prevents flooding from too much fuel as well as fuel starvation due to too low of a fuel level in the bowl. On Edelbrock carbs, the top of the carburetor needs to be removed to adjust the floats. Once removed, compare how low the floats hang when holding the top upright to the specifications in the owner's manual. Then turn the top upside down and measure the float distance to the carb top and compare the carburetor specifications. Adjustment is made by gently bending the float limiter tabs. An additional carburetor turning step is the carburetor jetting. Access to inside the fuel bowls (Edelbrock) or to the metering blocks/main body (Holley) is required to make changes. If the carburetor is providing too much or not enough fuel during idle, part throttle, or wide open throttle, after all of the previous tuning has been completed, the jets most likely need changed. Use the instructions in the owner's manual on proper selection. Edelbrock uses a specific combination for the primary jets with metering rods as they work together from idle to part throttle, located in their instructions. If a fuel adjustment is needed for the secondaries on either carb, jet replacement is required. There are additional tuning and adjustment options that may be required to further improve performance. The carburetor owner's manual will help you with those additional steps.

Depending on the carburetor model and which parts will be tuned, the cost for carburetor tools and components can range from under $10 to over $200 for an individual component up to a kit. The labor cost for carburetor tuning depends on the options available near you, their labor charge, and the number of hours required to complete.