Finding the right ratio of air to fuel will help extend the life of your engine. If the engine is not running smoothly, it is important to adjust this ratio and find the correct idle speed to reduce the pressure on the engine and ensure that it is not running too hard or too soft. Your car's carburetor can be adjusted in a few simple steps and without special tools.
Method 1 of 2: Adjusting the air-fuel mixture
Step 1. Locate and remove the air filter
Most cars require you to remove the air filter to access the carburetor for adjustments. Open the hood and make sure the engine is off before locating and removing the air filter. Unscrew the wing nut and other connections and remove the air filter completely.
Depending on the make, model and type of engine, the air filter can be located in different places in relation to the engine. Consult the owner's manual or workshop manual for your car
Step 2. Locate the adjusting screws on the front of the carburetor
There should be two screws on the front of the carb that are used to adjust the air/fuel ratio.
These set screws often resemble regular flat head screws. You can loosen and tighten them with a regular screwdriver to adjust the amount of fuel and air
Step 3. Start the engine and allow it to warm up to its normal operating temperature
Check the temperature gauge to see when the engine is at the correct temperature and listen to the sound of the engine to get an idea of what needs to be adjusted.
- An engine that is tuned too lean will ping at higher revs when you accelerate. More fuel needs to be added to the mixture.
- An engine that is tuned too rich won't necessarily make a different sound, but you'll be able to smell it. Reduce the amount of fuel a little.
Step 4. Adjust both screws evenly and find the correct mixture
Tuning a carburetor is like tuning a guitar or other stringed instrument. You have to turn the screws gently, evenly until you find the ideal position. Regardless of whether the engine is set too lean or too rich, first adjust it down (to a lean mixture) by turning both screws counterclockwise a quarter turn at a time. Then turn them slowly until you have an even and smooth mixture.
Adjusting the mixture is an imprecise art that requires you to know your engine well and listen to it carefully. Slowly tighten both screws and listen until the motor runs smoothly. An irregular sound or chatter is a sign that the mixture is too lean. Keep turning until you find the ideal position
Step 5. Replace the air filter
Replace the air filter after adjusting the carburetor and you are ready to ride again.
If you also need to adjust the idle speed, wait until you are done with replacing the air filter
Method 2 of 2: Adjust the idle speed
Step 1. Locate the throttle cable and idle speed adjusting screw attached to it
This is connected to the accelerator pedal, via the fan and the carburettor. As always, check the owner's manual or workshop manual for your make and model if you can't find the screws.
Step 2. Start the engine and allow it to warm up to its normal operating temperature
Let the engine warm up so that you adjust it under normal operating conditions, just like you did with the fuel/air mixture.
Step 3. Tighten the set screw
Do not turn the screw clockwise more than half a turn and listen to the motor. Most manuals state an optimal idle speed, although you do have some leeway if you want it a little higher or lower. Consult your manual to find this speed and check the tachometer while adjusting.
Step 4. Listen to make sure the motor is not running unevenly and adjust if necessary
It should take about 30 seconds for the bike to adjust to the changes you're making, so don't get too excited that could cause you to tweak too much. Turn slowly and listen carefully to the engine's response.
Step 5. Replace the air filter and finish the job
Shut off the engine and replace the air filter to finish the job, after adjusting the idle speed to the correct setting (or to your liking).
- If the engine does not run smoothly after adjusting the idle speed, go back to adjusting the air/fuel ratio and repeat the steps for adjusting the air-fuel mixture and the idle speed.
- Tightening the adjusting screw will increase idle speed, while loosening it will lower idle speed.
- If your car has a tachometer, you can use it to set the idle speed. Consult your manual for the correct speed.