The main carburettor parts play a critical role in the workings of small engines. The carburettor’s function is to mix fuel and air and then send it to the engine’s cylinders. These cylinders ignite the mixture using spark plugs or an equivalent, which is what powers the engine. Common outdoor power equipment use various types of carburettors. These include lawnmowers, leaf blowers, chainsaws and small generators.

JAK Max is a specialist wholesaler of carburettor parts and accessories for outdoor power equipment. We have a wide selection for all types of carburettors, including:

  • Float-type carburettors – these use a float chamber to ensure a constant fuel level and a steady supply to the engine.
  • Diaphragm carburettors – this type has a flexible diaphragm rather than a float chamber to control the fuel flow. Chainsaws, weed trimmers and other small engines use them when a float-type wouldn’t work due to engine vibration.
  • Variable venturi carburettors – the venturi tunnel is the narrow part of the air passage that increases the speed of the fuel and air mixture as it passes through. This kind of carburettor automatically regulates the size of the venturi tunnel based on engine demand to improve performance and fuel efficiency.

Only 20 minutes from the Melbourne CBD, we have 14 years of experience, industry knowledge and networking with the world’s top carburettor parts suppliers. 

Here’s our guide to the main parts of carburettor and their functions. We’ll cover all the carburettor components, explain the role of each, and give you some maintenance tips.

The Main Carburettor Parts Explained

Below is a carburettor diagram, with the primary carburettor part names highlighted.

Let’s discuss these carburettor parts in turn.

1. Venturi Tube

The carburettor venturi tube is a narrow point in the vertical carburettor pipe. It serves to speed up the flow of the fuel and oxygen mixture. As it passes through the constriction, the mixture is forced to move faster. This reduces the pressure in the area, creating a partial vacuum.

As nature abhors a vacuum and has to fill it, it does so by sucking in fuel from the carburettor’s float chamber and air from its air chamber at the top. The venturi tube is one of the carburettor components that plays a central role in ensuring that the cylinders receive the right balance of fuel and oxygen for optimal combustion and engine performance.

2. Float Chamber

A float chamber functions to automate and regulate the supply of fluid in an engine. Thus a carburettor float chamber measures and regulates the amount of fuel going to the engine’s cylinders.

All float chambers work on the same principles. In fact there’s even one in your toilet’s cistern, so you can watch it in action for yourself. The float chamber contains a hollow chamber floating on top of the fuel (like the big ball in your cistern.) This is linked by an arm to an inlet valve that controls the fuel intake. 

When the float chamber is filled, the fuel makes the float move upwards, causing the float arm to close the valve. As the level of fuel drops, so does the float, and the arm opens the valve to allow fuel to flow into the float chamber. These carburettor parts enable the float chamber to keep a consistent fuel level and pressure, and create a steady rate of fuel supply into the carburettor.

A stable fuel flow rate is critical for smooth engine operation and performance, and provides optimum fuel efficiency. An inconsistent flow can create combustion problems, loss of power and a misfiring engine.

Troubleshooting float chamber issues

Here’s how to detect and solve the most common issues with float chamber carburettor components:

  • A sunken or stuck float – check if the float moves freely after removing the carburettor bowl. If it’s still stuck, thoroughly clean it and remove any foreign debris. Also check your service manual to set the correct float level height so that the fuel supply is neither too rich nor too lean. You can do this by bending the small metal tab on the float.
  • Faulty needle valve – the needle valve regulates fuel entry. If it’s worn it can allow excess fuel into the mixture, which causes flooding. If stuck closed, it causes fuel starvation. You can use a carburettor cleaner to clean the needle valve and seat. If this doesn’t solve the problem, you can easily get replacement float needle valves from JAK Max.

3. Jets

Carburettor jets are small brass fittings positioned between the float chamber and the venturi tube. They control the amount of fuel flowing into the carburettor housing as it’s sucked through the venturi tube into the jets.

There are four main types of carburettor jets:

  • Main jet – this jet opens to control the fuel flow when you open the engine’s throttle to 50% – 100% power
  • Idle jet – a small fuel measure jet that regulates fuel flow when the engine is idling or running at low speed. It ensures smooth engine running when the engine throttle is closed.
  • Jet needle – this controls the flow of fuel when you both open and close the throttle. It functions within a range of 20% – 80% throttle power.
  • Needle jet – the jet needle enters and exits this jet as it regulates fuel flow.

The main jet also functions to regulate the fuel-air mixture and ensure that the correct air-to-fuel ratio reaches the engine. The size of the jet can affect this, depending on the circumstances. 

A small jet restricts the fuel flow, resulting in the fuel-air ratio containing more oxygen. This can increase fuel economy, but at the expense of engine power.

A larger jet allows more fuel to enter the venturi tunnel, which increases engine power, but decreases fuel economy.

4. Throttle Valve

The carburettor throttle valve is also called a piston valve. It’s one of the most important carburettor components, as it regulates the air flowing into it. 

This is a butterfly valve that works alongside the main jet, in response to accelerator pedal or engine throttle changes. The main jet will open when the throttle valve opens in response to increased pressure on the throttle. This allows the venturi tube to pull fuel from the main jet at the right rate compared to the airflow to maintain a steady fuel-air ratio.

The throttle valve is linked to the engine’s accelerator pedal by a spring-loaded arm. It’s a simple, direct mechanism that causes the arm to open the butterfly valve when the accelerator is depressed. A smooth and precise throttle response is crucial to ensure that the optimal fuel- air mixture is instantly available to the engine, so it can perform the required task optimally. This also helps with engine durability.

5. Choke

The carburettor choke is also a butterfly valve. Its role is to reduce the amount of air going into the carburettor so that the fuel-air ratio is richer in fuel. This allows a cold engine to be started more easily.

The effect of the choke restricting airflow is that this lowers the intake manifold pressure, causing more fuel to enter the carburettor. It’s the partial vacuum effect in action again.

Engines can either have a manual or an automatic choke. The difference between them is exactly what you’d expect. A manual choke has a lever that the user pulls to activate it, while an automatic choke is connected to the accelerator by a metal spring. This opens a choke plate when the accelerator is fully depressed before starting the engine.

6. Idle System

The carburettor idle system is responsible for monitoring the fuel supply when the engine is idling. This is necessary because when the engine is running at low RPM, the throttle is almost closed. This lowers the speed of the air flowing into the carburettor, which can interfere with the air-fuel mix and cause stalling.

The idle system is basically the whole passage from the float chamber to the venturi tube in the carburettor. It enriches the fuel mixture when the engine is idling to keep the engine running smoothly.

You can control the idle mixture using the idle mixture screw, typically located on the side of the carburettor. You can adjust the mixture and the idle speed control by turning the idle mixture screw counter-clockwise – you won’t need more than one to one-and-a-half turns.

Improper idling can not only interfere with current performance but can also lead to long-term engine degradation.

7. Linkages and Springs

Carburettor linkages are essentially the mechanical arms of the system that open and close valves, for instance. Carburettor springs are used in conjunction with the linkages to enable certain automated movements and ensure that they maintain their proper positions.

A carburettor uses a variety of differently shaped and angled linkages to connect its components and control its systems. The aforementioned linkage that allows the float in the float chamber to open and close the fuel intake valve is an example

Springs reinforce the linkages to ensure that the carburettor components stay in the correct position. They also allow the arms to snap back quickly from extended positions, in which case they are known as return springs. 

Similarly, springs help the carburettor’s valves to return to and maintain their closed positions when required to balance the air-fuel ratio. This combination of carburettor components allows for higher stability and contributes towards a smoother throttle response by acting as movement regulators. 

Worn-out carburettor springs can seriously affect performance. If the throttle return spring is weak, it can cause delayed throttle closure that creates unreliable, jerky acceleration. Similarly, if the idle mixture spring is worn, the idle mixture screw can move, which creates an imbalanced fuel-air mixture. This can cause stalls, rough idling and fuel wastage.

8. Gaskets and Seals

There are various types of carburettor seals, all with the same function – to do precisely what their name says. For example, dirt plug seals stop any undesired material from entering the carburettor. Throttle valve seals prevent air from leaking into the system, disturbing the air-fuel ratio.

Carburettor gaskets are a type of seal that specifically prevent air or fuel leakage between the carburettor and the engine. These are two small but vital carburettor parts that ensure optimal engine performance and the integrity of the entire system. So it’s important to recognise any signs of worn gaskets. 

Look out for:

  • Overall power loss – a lack of power, power surges when the throttle is steady, or engine backfiring.
  • Fuel leaks – any fuel dripping or a stronger than usual fuel smell near the engine. Black exhaust smoke is another indicator, and you may also notice lower fuel economy.
  • Vacuum leaks – if the venturi tunnel is compromised, a vacuum leak can occur. Watch for hard starting, high engine revving or sluggish acceleration.

If you experience any of these, your nearest JAKMax store will have a wide selection of top-quality carburettor gaskets.

9. Fuel Inlet and Fuel Filter

The carburettor fuel inlet is the entrance to the carburettor to which the fuel inlet lines attach, thus feeding fuel to the carburettor. The fuel goes directly into the float chamber, and the fuel inlet regulates the flow rate.

A fuel filter prevents debris from entering the carburettor by removing foreign objects like rust particles or dust from the fuel. It’s one of the most critical elements of the system, not only to protect the carburettor from wear and tear but also to ensure clean fuel. 

Cleaning your carburettor fuel filter: Close the fuel valve and remove the fuel filter by unscrewing the fuel inlet fitting. Remove any visible debris with compressed air or a soft cloth. If it’s badly clogged, soak it in carby cleaner and let it dry before refitting.

Replacing your carburettor fuel filter: turn off the fuel supply and take out the air filter. Insert the new air filter and open the fuel supply. Check for visible leaks. If you can’t see any, start the engine and let it idle. This should sound smooth. Finally, rev the engine to check that it responds immediately.

10. Mounting and Air Cleaner

The carburettor is mounted on top of the engine. In a typical configuration, it sits on the cylinder head, between the intake manifold and the air cleaner. Proper mounting is important to establish the carburettor’s correct place in the fuel and air supply chain, to ensure that the right air-fuel mixture reaches the cylinders. 

The carburettor air cleaner is the large round disc with ruffled edges that you’ll usually notice first when opening a car bonnet. Its role is to filter out impurities like dust and regulate air flow into the carburettor. This helps prevent dirt from clogging the carburettor components.

Types of Carburettors and Differences

Different types of carburettors are made to fit the needs of various engine applications. They’re designed to give each kind of user the optimal balance between efficiency, performance and control.

Simpler engines like chainsaws and lawnmowers are best suited for float-type carburettors, only needing basic fuel supply control. Chainsaws can also benefit from compact diaphragm carburettors. These are typically used in smaller engines working under variable conditions, as this type provides a more reliable fuel-air mixture in these situations. They’re common in scooters and lower-powered motorcycles. 

Variable venturi carburettors are more often found in faster bikes and cars, as they allow constant adjustment of air-fuel mixture at higher RPMS. They can also operate across a broader range of speed and load. 

Piston-engine aircraft also use carburettors, usually float-type or diaphragm type. They will normally be enhanced by capabilities like automatic altitude compensation to keep the fuel flow rate constant as they climb and descend.

Common Carburettor Issues & Maintenance Guide

Here are some quick tips for dealing with the most common minor issues you’ll encounter with carburettors:

Clogged carburettors

Warning signs:

  • Engine won’t start
  • Erratic idling
  • Lagging acceleration
  • Unusually high fuel consumption

How to fix:

  1. Shut off the fuel supply and remove the carburettor.
  2. Drain all the fuel and remove the float bowl or diaphragm.
  3. Take off the jets and clean them with carby cleaner.
  4. Use carby cleaner and a small brush, or compressed air, to clear internal fuel passages.
  5. Clean the float valve and needle, removing any fuel residue. Check both for damage.
  6. Reassemble and reinstall the carburettor.

Worn gaskets

Warning signs:

  • Fuel leaks
  • Higher RPMs or stalling (indicating a vacuum leak)
  • Visible cracks

How to fix: Replace with a new gasket or gasket set from JAK Max.

Worn jets

Warning signs:

  • Lagging acceleration
  • Stalling when idling
  • Abnormally high fuel consumption
  • Misfiring at certain RPM ranges

How to fix: Use compressed air or carby cleaner to clean them. If they’re damaged, pop down to your nearest JAK Max store for some replacement carburettor jets.

Worn float valve

Warning signs:

  • Fuel leaks
  • Stalling or sluggish acceleration
  • Fuel flooding when starting the engine

How to fix: adjust the float height according to the user manual. If necessary, you can replace the float valve.

Worn seals

Warning signs:

  • Poor engine performance caused by air leaks
  • Fuel leaks or a strong fuel smell
  • Delayed throttle response

How to fix: check the seals for cracks or other wear – if you see any, get some new carburettor seals from JAK Max, or a handy float valve and seal kit.

Best practices for carburettor cleaning and maintenance

It’s easy to keep your carburettor in good nick. Always use clean, fresh fuel – you can add a fuel stabiliser if you wish. Drain the carburettor of any excess fuel after each use. Regularly inspect the gaskets and seals, and replace them at any sign of wear and tear or damage or if you see any fuel leak. Clean the air filter regularly too, as well as the fuel lines and jets.

Carburettor Parts and Brands Available at JAK Max

JAK Max carries a wide choice of carburettor components from top brands, including well-known motorcycle carburettor parts names and car carburettor parts names.

We offer a full-spectrum carburettor parts list:

  • Carburettor bowls
  • Carburettor floats
  • Float bowl assemblies
  • Filter bowl assemblies
  • Diaphragms and diaphragm kits
  • Fuel filters
  • Float bowl springs
  • Spring metering levers
  • Valve inlet needles
  • Float valve needles
  • Needle and seat kits
  • All gaskets, plus gasket kits
  • Check valve screens
  • Seal intake manifolds
  • Throttle valve assemblies
  • Carburettor primers
  • Throttle shafts
  • Metering valves
  • Primer bulbs
  • Carburettor assemblies

Carburettor Parts FAQs

What are the parts of a carburettor?

The main carburettor parts are:

  • Float bowl/chamber – maintains a consistent amount of available fuel.
  • Float – controls the fuel level in the bowl.
  • Needle valve – controls the fuel entering the fuel bowl.
  • Main and idle jets – control the amount of fuel going into the air/fuel mixture.
  • Throttle valve (or throttle plate) – controls the amount of air and fuel entering the engine.
  • Air intake – allows air to enter the carburettor to create the fuel/air mixture.
  • Choke – temporarily enriches the fuel-air mixture to help with cold weather starts.
  • Accelerator pump – provides a richer air-fuel mixture when you increase the throttle.
  • Venturi tunnel – creates a vacuum to speed up the fuel flow into the air flow.
  • Mixture screw – regulates the air-fuel mixture at low speeds and when idling.
  • Throttle linkage – links the engine accelerator to the carburettor.

What is the function of venturi in a carburettor?

The venturi tube is a narrowing in the carburettor pipe that creates a vacuum, which speeds up the flow of the fuel and oxygen mixture. It helps to maintain the optimal balance of fuel and air as it’s fed into the combustion chamber of the engine.

How does a carburettor fuel valve work?

The carburettor fuel valve is responsible for managing the fuel flow from the fuel tank into the carburettor. It’s also called a fuel shut-off valve. On a small engine like a lawnmower it can be manually operated. 

What are the types of carburettors?

The three main types of carburettors you’ll come across are float-type carburettors, diaphragm carburettors and variable venturi carburettors. The float type is the one you’ll most commonly find in lawnmowers and handheld garden equipment like chainsaws. More powerful equipment and motorcycles typically use one of the latter.

Is the carburettor part of the engine?

The carburettor isn’t an actual part of the engine. Rather, it’s part of the fuel system that supplies it. Its role is to control the fuel/air mixture that’s fed to the engine.


Explore the vast selection of carburettor parts at JAK Max. Whatever you need, whenever you need it, just find your nearest JAK Max dealer.