10 Bad Carburetor Symptoms & Replacement Cost

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bad carburetor symptoms

Whenever your older vehicle is not performing as expected, several possible causes might be. Its carburetor is one of such components. Carburetors aren’t longer utilized in contemporary automobiles in various situations, although they are still used in older cars.

A carburetor effectively started and ran the car during the mid-’70s and early automobiles, such as vintage or show vehicles. Such carburetors would combine air and fuel to create the ideal combination before delivering it to your engine for its internal combustion.

Such carburetors became the most critical automobile component since they ensured that it ran at full performance without being overly rich or low. While improved technology has replaced the need for carburetors in contemporary automobiles, thousands of cars on the roads depending on such carburetors.

As with any other component on a car, carburetors may become poor or malfunction, prohibiting the vehicle from functioning correctly. This is why understanding the signs of a failed, or defective carburetor is critical for car ownership.

To help you in determining whether you are experiencing some bad carburetor signs and symptoms, the following are indicators you can examine to get your car serviced immediately before the situation worsens.

Symptoms of a Bad or Failing Carburetor

  • Reduced Engine Performance
  • Overheating or Backfiring Engine
  • Black Smoke
  • Hard Starting
  • Rough Idle
  • Poor Acceleration
  • Hesitation Under Load
  • Carburetor Flooded With Fuel
  • Engine Running Lean
  • Engine Running Rich

What Is A Carburetor?


The carburetor is in charge of mixing the proper proportions of fuel and air and controls engine speed. For most times, a precise ratio of air/fuel mixture must be maintained, and your carburetor is among the elements that contribute to air/fuel ratio balance. Additionally, your carburetor is in charge of engine speed management.

Today’s automobiles utilize three distinct kinds of carburetors. They feature a one-barrel, a two-barrel, and a four-barrel carburetor. The engine configuration of your vehicle affects the sort of carburetor required. Typically, higher-performance engines might need a couple of carburetors to deliver the proper quantity of fuel.

Symptoms of a Bad or Failing Carburetor

It’s critical to understand the signs of a bad or failing carburetor to avoid expensive, unnecessary repairs. Additionally, it is essential to address the issue immediately, as a failed carburetor may result in a cascade of problems that can compromise your engine. Below are the most common symptoms of a bad carburetor.

Reduced Engine Performance

Whenever your automobile doesn’t appear to have the same level of power or engine performance as it once had, this might be due to a bad or failing carburetor. This is due to the carburetor distributing and analyzing a fuel/air mixture to your engine. This air/ fuel is necessary for your engine to work optimally. When your carburetor is failing, you will not only lose power in your automobile, but you might also discover that you are using too much fuel than usual and that acceleration is poor.

Overheating or Backfiring Engine

Backfiring? Overheating? Yes, this might also indicate a clogged or dirty carburetor. Suppose your carburetor is filthy or has a problem that permits it to provide a lean fuel mixture or even a mixture with insufficient fuel. In that case, your engine could overheat or backfire in certain circumstances.

Black Smoke

When you see black smoke emanating from your tailpipe, it’s also indicative of a faulty carburetor. It is because your engine might use an excessive amount of fuel, and that excess fuel burns off and produces black smoke. This can ultimately burn out your carburetor, requiring a replacement carburetor.

Hard Starting

A clear indicator of a carburetor issue is the hard starting of an automobile. The car could have difficulty starting in cooler temperatures but will restart right away once warmed up. The car might not even start and will keep cranking over in an attempt to start. These problems are caused by your carburetor not combining the correct quantity of fuel/air mixture. In this instance, it’s not supplying enough fuel to your engine whenever you try to start the car.

Rough Idle

Most of the time, a rough idle condition is caused by a highly lean fuel mixture, which leads to lean misfires. Idle difficulties are often caused by air leaks within your intake manifold gaskets and carburetor, as well as vacuum lines air leaks, the PCV system, and the EGR valve.

Some carburetor-related issues involve an idle mixture adjustment set too lean, which could be corrected by backing out one-quarter turn of its idle mixture adjustment screw or bolt at a period until your idle quality improves.

Another carburetor trouble is a dirty idle mixture circuit that could require rebuilding or cleaning using a carburetor cleaner. Also, a faulty purge control valve that isn’t shutting and leaking fuel vapors straight back into your carburetor is another potential reason for a rough idle, but it is not very frequent.

Poor Acceleration

While accelerating, delay or hesitation is among the most telltale signs of a faulty carburetor. This is usually caused by an overly lean fuel mixture, which means there’s not enough fuel and too much air. Worn throttle shafts, faulty or weak accelerator pump, or debris within your carburetor are all possible causes of a poor air/fuel mixture.

Hesitation Under Load

Stumble or misfire happens when the engine is under load due to a faulty power valve inside the carburetor, which is called a hesitation. The carburetor pulls fuel throughout its metering circuits with the help of an intake vacuum. The intake vacuum diminishes as engine load increases and the throttle is opened widely.

Because this may cause the fuel/air mixture to become lean, the power valve incorporates a vacuum-sensing diaphragm loaded with springs that open to increase fuel flow once the vacuum falls. This valve must be changed when the diaphragm fails or is clogged by fuel varnish deposits and debris.

Carburetor Flooded With Fuel

Your needle valve is impossible to shut if its fuel bowl is dirty. Fuel could flood your carburetor as a consequence. As a result, after refilling your carburetor, any excess fuel leaks via the carburetor bowl vents, soaking your spark plugs. This shows how hazardous a dirty carburetor can be, resulting in a fuel-flooded engine and other problems. Also, Flooding could also be caused by excessive fuel pressure because it drives the gasoline past the carburetor’s needle valve.

Engine Running Lean

The vehicle running lean is another typical indicator of a dirty or faulty automobile carburetor. If your automobile makes a sort of sneezing noise, it signifies it is leaning. Lean fuel mixture implies that the engine isn’t supplying sufficient fuel to your carburetor, resulting in an unbalance in the 12:1 air/fuel ratio. If the air/fuel ratio balance is wrong, your engine will run lean.

Engine Running Rich

Another indication and symptom of a dirty or defective carburetor are that your engine begins to run rich. When a rich fuel mixture, there is either not enough air or too much fuel within your carburetor. If you notice black smoke streaming from your tailpipe, this indicates a rich fuel mixture in your carburetor, and it’s burning the excess fuel, resulting in black smoke.

What To Do?

Since the carburetor influences older automobiles in so many ways, it’s critical to fix the problem asap! It’s essential to get the carburetor examined or serviced by a professional to diagnose and repair the issue appropriately. There are different options you can do when it comes to restoring a malfunctioning carburetor.


Cleaning your carburetor using a strong carburetor cleaner is among the first tasks a mechanic would do. Quite often, your carburetor malfunctions due to dirt or debris having gotten into its internal components and obstructed the jets or floats.

This hinders your carburetor from supplying the necessary fuel/air mixture to your engine, producing a slew of issues with the car. To solve the problem, the carburetor will be disassembled and cleaned completely using a carburetor cleaner to eliminate any unwanted particles.

Rebuild or Replace

If a cleaning remedy fails to cure the malfunctioning carburetor, it might be one or more of the carburetor’s pieces requires to be replaced. The fuel bowl, needle, float, and other carburetor components operate together to achieve the correct air/fuel ratio. Neither of the surrounding parts will function correctly if one of these parts fails or is broken.

Carburetor Adjustments

Once your engine has reached the normal operating temperature, modify its idle mixture adjustment screws and idle speed. Set its idle mixture screws for the finest idling and set its idle speed to standards (usually 600 to 650 rpm). Set every idle mixture screw in till your engine stutters, then reverse it out a quarter to half turn. Proceed to fine-tune your idle for the optimum ride.

Its automatic choke might also need adjustments whenever your engine doesn’t start properly. The choke must be entirely closed with a cold engine, and after the engine warms up, it must be fully open. Slight adjustments go a pretty long way, and getting the choke housing exactly fine could take multiple trial-and-error changes.

When your engine stutters or hesitates while accelerating, its accelerator pump linkage or its cam might need to be adjusted too to boost the amount of fuel sprayed into your engine whenever the throttle is opened. If your cam or accelerator pump linkage has many adjustment options, attempt the following higher setting if additional fuel is required.

Carburetor Repair and Replacement Cost

The decision to replace or rebuild your carburetor is based on your mechanical abilities, funds, time, and the amount of your carburetor problems. Always look into the cost of a brand new carburetor. A few extra dollars invested in a replacement carburetor component could sometimes spare you the time and effort of repairing and cleaning your existing carburetor.

Carb Replacing

If indeed, your carburetor has substantial deterioration or significant damage that cannot be repaired by cleaning or reconditioning, it should be replaced.

  • Cost: range from $20 up to $200 (DIY) $70 per hour + $20 up to $200 per component (Professional Fee)
  • Duration: 30 up to 45 minutes
  • Difficulty: Moderate
  • Task: Uninstall the old carburetor assembly and replace it with the new one.

Carb Rebuilding

New gaskets and various required components are included in a carburetor rebuild kit to revitalize your carburetor. Always make sure you get the correct carburetor kit.

  • Cost: Range from $10 up to $60. (DIY) $70 per hour + $10-$60 per portion (Professional Repair Fee)
  • Duration: 1.5 up to 2 hours or more
  • Difficulty: Mechanical Expertise
  • Task: Rebuild, Install after removing, disassembling, cleaning, and replacing components.

Rebuilding Tips

Before disassembling your carburetor, consult your service handbook for an assembly chart to use as a guide. Specific carburetor kits don’t come with a schematic or directions for assembly. Also, keep in mind where the various vacuum hoses and pipes to your carburetor connect. If necessary, draw a diagram or mark all hose connections.

Collect your components on a clean desk, steel tray, or piece of paper. Make a list of how the parts came off so you remember how to put your carburetor again together. Keep an eye out for the little check balls. Utilize a carburetor cleaner or solution that will not harm plastics or delicate metals. Put on rubber gloves to avoid skin interaction with chemical solvent or cleaning. To prevent inhaling fumes, follow the cleaning directions carefully and in a well-ventilated location.

Examine your throttle shaft for signs of wear. A damaged throttle shaft hole enables air to be drawn in past the shaft, causing the fuel mixture to lean out. Disconnect the throttle shaft, enlarge the hole using a drill bit, and replace it with a metal or copper sleeve to restore proper clearances.

Another thing to look for is a faulty float in your fuel bowl. For copper floats, shake to see whether there’s fluid inside. Fuel gets into the float via a small hairline fracture in the seam, leading it to sink and flooding your engine with too much gasoline.

The issue with plastic floats is that they absorb gasoline over time, allowing the float to sit too low in your fuel bowl, thus flooding your engine. The problem might be resolved by replacing a faulty float.

Installation Tips

Tidy the mounting area on your intake manifold before putting a new gasket beneath your carburetor. The old gasket should not be reused since it nearly always leaks! To reduce the risk of air leakage, apply a gasket sealer, but don’t utilize RTV silicone since it dissolves whenever it comes into touch with gasoline.

Replace the gasket. Ensure that your carburetor base mounting nuts and bolts are equally tightened to ensure that the gasket is securely fastened in place. Overtightening the bolts might cause your carburetor base plate to break or deform.

Be careful not to cross-thread their fittings when rejoining the fuel line or any other connections like the EGR and PCV to your carburetor. Overtightening these threads in its soft casting might cause them to strip. Ensure the throttle return springs on the throttle linkage are reattached. Once you start your car, you don’t want to wind up with such a runaway engine.

Whenever springs get rusted and worn, change them with new ones. Also, make sure your throttle linkage is in good working order. While installing your air cleaner, be careful not to overtighten the nut that holds it in place, as this might distort and harm your carburetor’s casting.

All fasteners and rubber fuel hoses should be inspected. Any damaged, leaking, brittle, stiff, or mushy hose should be replaced. All vacuum and exhaust hose connections, fuel lines, throttle links, and return springs should be double-checked. Start your car and check for any other problems or leaks.


It’s critical to bring your car to an auto repair shop as soon as you notice any mentioned symptoms above. Ignoring these signs is a waste of money. Since a faulty carburetor has a direct impact on your car’s fuel economy, you’ll catch yourself paying more money at the gas station. Engine failure might be caused by an incorrect fuel/air mixture.


What happens when the carburetor is bad?

A carburetor is the principal component of your engine responsible for measuring and supplying the air/fuel balance necessary for it to operate. An engine with such a defective carburetor could have poor acceleration and a significant loss of power and fuel economy.

Can you clean a carburetor without removing it?

Yes, you can; here’s how to clean your carburetor without dismantling it: Put on safety equipment, turn off your engine, and remove its air filter housing, as well as any hoses or connections and its bottom bowl. Using a vacuum, remove any loose debris, grime, dirt, dust, and other particles from the surface.

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