



By N2H

Carburetor Tuning - Health is Wealth

aka carburetor, carburetter, carburettor, carb or carby

There are three basic functions a carburetor must be able to perform. First, it should be able to supply fuel to the airstreams in tiny droplet forms. Second, it must take charge of how many revolutions per minute an engine should make. And third, it must be able to keep the ratio of air to fuel mixture consistent. All these functions are interdependent with each other.

In tuning a carburetor, the first thing to do is to set the correct idle speed. It is advisable to set the idle opening to minimal. There is no universal idle setting for engines. Depending on the camshaft profile, varied quantities of air are needed for idling.

Carburetor tuners usually drill holes on the butterfly valves in tuning idle speed. However, these holes are permanent so they will be a problem when you decide to use the carburetor in another engine. An alternative to this method is to place a jet on the middle of the base plate, which makes it easier to increase or decrease the amount of air. This process is referred to as idle air bypass, which is useful for big cams. The goal here is to get the engine idling at the highest possible speed, while the butterflies are closed.

Once you’ve got this done, then you can experiment with the idle screws to find the optimum idle speed. When you step on the gas and the engine does not choke, you have reached a consistent idle speed.

However, if you’re not confident with your adjustments, remember that a rich mixture is better than lean mixture. Lean mixture can cause damage to your engine, while rich mixture will only result to power loss.

To adjust air to fuel ratio, you basically have to modify the main jet. Larger jet orifice size means having more fuel in the ratio, while if jet is smaller fuel is less also.

Tuning a carburetor to get more air flowing in the main circuit should be done by carb experts or serious tuners only. Altering the air bleed will change the needs of the main jet. To get a lean mixture, you would need larger bleed. However, this can affect the function of the main circuit and change the fuel curve. This procedure is accomplished by drilling on stock carburetors, while air bleed can be replaced on race carburetors.

High-end carburetors allow booster replacements. In most cases, booster change also means changing the venturi because both should match. Both of these components are responsible in the pressure variations that bring fuel to the main circuit.

Again, to get a carburetor correctly tuned, have it done by carburetor tuners or professionals racers who are deeply technical and skilled in this area.

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