The job of a carburetor is to prepare the fuel/air mixture that is then delivered to the combustion chamber and ignited there. The golden age of a carburetor lasted until the beginning of 1980s when computer controlled fuel injection began to be used to increase fuel efficiency, improve performance and reduce emissions.
If your vehicle was manufactured three or four decades ago, most likely it is equipped with a carburetor or even two. Regardless of its design a carburetor can easily get out of whack, so here is the guide of how to find out when it needs a replacement or adjustment.
Signs of a bad carburetor
Just about any carburetor problem can be diagnosed based on the behavior of your engine.
Your engine is hard to start
If your classic vehicle is hard to start when the engine is cold, this means that your fuel/air ratio is out of norm and too lean. It can be fixed by an adjustment of the choke mechanism that could get stuck or another simple carburetor modification.
Unusual or rough idling
If you experience no problem with starting your car but it idles roughly or not smoothly then it may alert you of one of the following carburetor problems.
If your engine idles too slowly or it begins to shake and sputter when you release the gas pedal this means that your fuel/air mixture is either too lean or rich.
In case its RPMs are too high when idling, especially after you release the accelerator, this may be a sign of the sticking choke inside the carburetor. Sometimes, you may just need to adjust the idling speed.
Your engine stalls
If your engine stalls when idling, this usually says that your carburetor experiences a lack of fuel or the idle speed needs to be adjusted.
If you push down the gas pedal but your engine hesitates or stumbles instead of accelerating, most likely the carburetor doesn’t supply enough fuel when the engine needs it most.
Increased fuel consumption and/or black smoke from your exhaust
If the mentioned above is the case, there is a chance that your carburetor supplies more fuel than the engine needs. When the fuel/air mixture is too rich the extra petrol can’t be burned in the combustion chamber and is thrown out through the exhaust system. Don’t ignore this problem as this increases pollution, wears out your spark plugs and wastes your money at the pump.
How to fix a bad carburetor
If you don’t have necessary experience and you’re not a professional mechanic, allow your mechanic to fix the carburetor as you can make things worse trying to do the trick yourself.
How it works
In plain English, a carburetor is a metering valve that mixes air with fuel and supplies it to the combustion chamber. Since an engine is very sensitive to an improper mixture, the carburetor must be able to provide the right amount of fuel and air at any RPMs.
The harder you push the gas pedal the more air passes through the carburetor and therefore more fuel is sucked with air. Once you release the accelerator, the airflow reduces, so less fuel is pulled through resulting in less engine power.
Regardless of a carburetor design it is a complex device with many moving parts and passages that may clog. It is equipped with a choke mechanism to make it easier for you to start the engine in cold weather. Just like your toilet, it has a float valve that maintains the right level of fuel within the carburetor. Besides, it has a lot of linkages, rubber and plastic parts that may go out of service and malfunction.
At the end of their era carburetors were supplied with crude emission controls which made them inefficient. Fortunately, the introduction of fuel injection has eliminated this problem.