Even with the advent of modern fuel injection, Carburetors are still a major component of a lot of outboard motors today.
The carburetor is responsible for mixing the fuel and air in the correct proportions before feeding it into the engine cylinders, where it is ignited to produce power. The carburetor also controls the amount of fuel and air that enters the engine, which determines the engine’s speed and power output.
Without a well-functioning carburetor, your outboard motor may suffer from poor performance, low fuel efficiency, and even damage to the engine. Therefore, it is beneficial to understand how your carburetor works and how to maintain it properly to keep your outboard motor running smoothly.
Warning!
Just a quick disclaimer, Carburetors are a major component of an outboard motor and are responsible for fuel delivery and as such proper care should be taken when playing with fuel and major components.
Please consult your local marine mechanic if you are not comfortable working on these systems, as petrol fuel can explode and the risk of personal injury and damage to these fragile components is high.
How a carburetor works
The carburetor works by drawing fuel through the fuel line and mixing it with air in the carburetor’s venturi tube. The fuel and air mixture is then delivered to the engine cylinders through the intake manifold, where it is ignited by the spark plugs to produce power.
The carburetor’s main components include the float bowl, the main jet, the idle jet, the choke, and the throttle valve. The float bowl holds the fuel and contains the float and needle valve, which regulates the fuel level in the bowl.
The main jet controls the amount of fuel that flows through the carburetor at high speeds, while the idle jet regulates the fuel flow at low speeds. The choke is used to enrich the fuel mixture during cold starts, while the throttle valve controls the amount of air that enters the engine, which determines the engine’s speed.
Common carburetor issues
Carburetors are an essential component of your outboard boat engine. They play a critical role in regulating the fuel and air mixture that powers the engine. However, like any mechanical part, they are prone to problems that can impact the performance of your engine. Here are some of the most common issues with outboard carburetors.
- Clogged Fuel Jets: One of the most common issues with outboard carburetors is clogged fuel jets. Dirt, debris, and other contaminants can accumulate in the fuel system and block the flow of fuel to the engine. This can cause the engine to run poorly or not start at all.
- Stuck Floats: Another issue that can occur with outboard carburetors is stuck floats. Floats are responsible for regulating the flow of fuel into the carburetor. If they become stuck, fuel can overflow into the engine, causing it to flood and run poorly. Old floats can crack and fill with fuel which will also give you the same symptoms as a stuck float.
- Worn Needle Valves: The needle valves in the carburetor control the flow of fuel into the engine. Over time, they can become worn or damaged, which can cause the engine to run rich or lean.
- Damaged Gaskets: Gaskets are used to seal the various components of the carburetor. If they become damaged or worn, air can leak into the system, causing the engine to run poorly.
- Dirty or Blocked Air Filters or Air Box: The air filter or air box attached to the carburetor plays a critical role in ensuring that the engine receives the proper amount of air. If the filter or box becomes dirty or clogged, airflow can be restricted, causing the engine to run poorly or not start at all.
Fuel issues
bad fuel can have a significant impact on the performance and efficiency of an outboard carburetor. It can lead to various problems, including clogged jets, damaged fuel lines, and corroded carburetor components. Let’s take a closer look at how bad fuel affects outboard carburetors and what you can do to prevent these issues.
What is bad fuel?
Bad fuel is any petrol that contains contaminants, such as water, dirt, rust, etc. It can also be fuel that has been sitting in storage for an extended period or has been exposed to extreme temperatures. Bad fuel can cause problems for any engine, but it can be particularly damaging to outboard carburetors.
How bad fuel affects outboard carburetors
Clogged jets: Bad fuel can cause clogged jets in the carburetor, which can prevent the proper flow of fuel and air. Clogged jets can lead to poor acceleration, rough idling, and decreased power. The buildup of deposits can also cause the carburetor to run lean, which can lead to engine damage.
Damaged fuel lines: Bad fuel can also damage the fuel lines that supply fuel to the carburetor. The impurities in the fuel can cause the fuel lines to become clogged or corroded, leading to fuel starvation and engine failure.
Corroded carburetor components: Bad fuel can also cause corrosion in the carburetor’s metal components, such as the float bowl and needle valve. Corrosion can lead to leaks, which can cause fuel to spill into the engine and damage internal components.
Preventing bad fuel-related issues
The best way to prevent bad fuel-related issues is to use high-quality high-octane-rated fuel and maintain a regular maintenance schedule. Using a fuel stabilizer can also help keep fuel fresh during storage periods.
How to make adjustments on an outboard carburetor:
If you own an outboard motor, you know that the carburetor plays a crucial role in keeping it running smoothly. But over time, adjustments may need to be made to ensure optimal performance. Here’s a step-by-step guide to making adjustments to an outboard carburetor:
- Check the service manual: Before making any adjustments to the carburetor, consult the service manual for your specific outboard motor. It will have detailed instructions on how to adjust the carburetor and what settings to use.
- Locate the carburetor: The carburetor is usually located on the top or side of the engine, and it will have adjustment screws for the idle speed and air/fuel mixture.
- Adjust the idle speed: Start by adjusting the idle speed screw, which is usually the largest screw on the carburetor. Turn it clockwise to increase the idle speed and counterclockwise to decrease it. Use your tachometer to ensure that the idle speed is within the recommended range.
Adjust the air/fuel mixture: Before adjusting the mixture screw, wind it all the way in counting every half turn and make a note of this, this will give you a good baseline, you can cross-reference this with the service manuals recommendations to see how far out your settings were. Next, using your service manual’s recommended settings adjust the air/fuel mixture screw, which is usually located near the idle speed screw. Turn it clockwise to lean out the mixture (more air, less fuel) and counterclockwise to richen it (more fuel, less air).
- Test the engine: After making adjustments, start the engine and let it run for a few minutes. Listen for any unusual sounds or vibrations and check your tachometer to ensure that the idle and high-speed operation are within the recommended ranges.
Carburetor chokes
There are several types of choke mechanisms used in outboard carburetors. The most common are manual and automatic chokes. Manual chokes require the operator to pull a lever or push a button to activate the choke. Automatic chokes, on the other hand, are activated by various mechanisms that sense engine temperature.
automatic choke
Another type of choke mechanism used in some outboard carburetors is the enrichener valve. The enricher valve is a small valve that allows extra fuel to enter the carburetor when the engine is cold. This extra fuel helps the engine start, and the valve closes once the engine reaches operating temperature.
Finally, most outboard motors use a primer bulb to provide extra fuel to the carburetor when starting a cold engine. The primer bulb is located in the fuel line between the gas tank and the carburetor and is manually pumped to force fuel through the system
Preventing carburetor issues
To prevent issues with an outboard carburetor, it is important to perform regular maintenance and inspections. This includes changing the fuel filter regularly, inspecting the fuel lines for damage or leaks, and adjusting the carburetor as needed, (consult your service manual for a recommended service schedule).
Engines that have little use or get stored for long periods of time may need their carbureters cleaned out due to fuel sitting in the carburetor and going bad.
regular maintenance and inspections are key to ensuring the longevity and reliability of the outboard motor.
Here are some tips to prevent issues with your outboard carburetor.
- Keep it clean: Dirt and debris can easily clog up the carburetor, affecting its performance. Make sure to clean the carburetor regularly, especially if you use your boat in dirty or dusty environments. Use a carburetor cleaner and a soft-bristled brush to remove any buildup.
- Use the right fuel: Always use the recommended fuel for your outboard motor. Using the wrong fuel can cause the carburetor to malfunction and lead to engine damage.
- Change your fuel filters: The fuel filters help to prevent debris from entering the carburetor. Make sure to change the fuel filters regularly, as recommended by the manufacturer.
- Check the fuel lines: Fuel lines can become cracked or damaged over time, which can cause fuel leaks and affect the carburetor’s performance. Inspect the fuel lines regularly and replace any damaged lines.
- Adjust the carburetor: If your outboard motor is not running smoothly, it may be necessary to adjust the carburetor. Follow the steps outlined in the service manual to adjust the idle screw and ensure the fuel-to-air mixture is correct.
How to Clean an Outboard Carburetor
One of the most common problems with outboard motors is a dirty or clogged carburetor. A dirty carburetor can cause poor performance, reduced fuel efficiency, and even engine failure. Luckily, cleaning an outboard carburetor is a simple process that you can do yourself with a few basic tools.
Step 1: Gather Your Tools
Before you get started, you’ll need a few tools:
- Screwdrivers – Phillips head and flat blade
- Socket and ratchet set – ¼ inch
- Carburetor cleaner
- Compressed air
- Clean rags
Step 2: Remove the Carburetor
The first step in cleaning an outboard carburetor is to remove it from the motor. Start by disconnecting the fuel line and any electrical connections. Then, use a screwdriver to remove the carburetor from the motor. Use your service manual and follow the steps for the correct disassembly procedure.
Step 3: Disassemble the Carburetor
Once you’ve removed the carburetor, you’ll need to disassemble it. Take the carburetor apart carefully, making note of how the parts fit together. You may want to take pictures as you go so you can refer back to them later. Again follow your service manual for the correct disassembly procedure.
Step 4: Clean the Carburetor
With the carburetor disassembled, it’s time to clean it. Start by spraying carburetor cleaner on all the parts. Use a clean rag to wipe away any dirt or debris. Then, use compressed air to blow out any remaining debris. Be sure to clean all the small passages and jets.
Step 5: Reassemble the Carburetor
Once you’ve cleaned all the parts, it’s time to reassemble the carburetor. Refer back to your pictures or notes to make sure you put everything back together correctly.
Step 6: Reinstall the Carburetor
With the carburetor reassembled, it’s time to reinstall it on the motor. Reconnect the fuel line and any electrical connections. Then, start the motor and check for proper operation.
Conclusion
In conclusion, outboard carburetors are prone to a variety of issues that can impact the performance of your boat engine. However, with proper maintenance and care, many of these issues can be prevented. Using fresh fuel, cleaning when necessary, inspections, and replacement of worn or damaged components can help keep your carburetor and engine running smoothly.
Keeping your vessel in top shape doesn’t have to be difficult. Explore The Everyday Captain for more, actionable advice, step-by-step guides, and helpful resources designed to keep you safe, save you money, and make boating more enjoyable. Whether you’re tackling a repair, improving maintenance, or just learning the basics, The Everyday Captain has you covered.
