Rajan Wilcox
The Keihin PWK carburettor is used in a variety of motorcycles, including KTM, Husqvarna, and Yamaha models. Connecting the fuel lines correctly is essential for optimal engine performance. The process involves considerations such as jet sizes, flow rates, and proper routing of hoses to prevent fuel leaks and potential engine damage. It is important to use ethanol-resistant hoses and clamps to secure the fuel lines, ensuring safe and efficient fuel delivery to the carburettor.
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What You'll Learn
Hose job: T the identical vents on each side
When it comes to the Keihin PWK carburettor, the vent hose routing is a crucial aspect to consider. Each side of the carburettor features two vents, and the correct configuration of these vents is essential for optimal performance.
One suggested approach is to "T" the identical vents on each side. This means connecting the matching vents on the left and right sides of the carburettor using a T-shaped connector. This configuration allows for proper ventilation and helps maintain the desired air pressure in the system.
It is important to ensure that the vent hoses are directed appropriately. One suggestion is to route one hose down towards the swingarm, while the other hose is directed above the airbox. This setup helps to prevent fuel leakage and minimise the risk of dirt and debris entering the engine.
Additionally, it is recommended to keep the vent hoses below the air filter height. This precaution ensures that fuel does not leak onto the air filter when the bike is upside down or tilted at a significant angle.
By following these guidelines and ensuring proper ventilation, you can help maintain the performance and longevity of your Keihin PWK carburettor, while also reducing the risk of fuel-related issues and engine damage.
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Drain fuel from the carburetor to wash out any water or dirt
To drain fuel from the carburetor of your Keihin PWK carb, you will need to locate the carburetor drain screw. This is usually an angled bolt found at the bottom of the carburetor bowl, but it may also protrude from the side of the carburetor. Some models have two screws, while others have one. If you have a WEN closed-frame inverter generator, for example, you will see a Phillips-head screw above a drain hose.
Once you have located the drain screw, you can loosen it until gas starts flowing out of the carburetor and into a storage container. You may need to remove the screw completely. If you are unable to access the screw with your stock air box, you can try running the bike with the petcock off until it stalls, which will burn up any remaining fuel in the carb.
It is important to note that you should always drain fuel from the carburetor after washing your bike to wash out any water or dirt that may have entered the vents. This can be done by laying your bike over after washing to allow the fuel to drain out. Additionally, ensure that the hose ends are slash-cut to prevent dirt and mud build-up from plugging the hoses at the open end.
By following these steps, you can effectively drain the fuel from your Keihin PWK carb and maintain the performance and longevity of your motorcycle.
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Use clamps on fuel hoses and ethanol-resistant hoses
When connecting fuel lines for a Keihin PWK carb, it is important to prioritise safety and efficiency. To achieve this, always use clamps on your fuel hoses and opt for ethanol-resistant hoses.
Clamps are essential for securing the fuel hoses in place, preventing leaks and ensuring a tight connection. Leaking fuel can cause significant issues, including engine damage and safety hazards. By using clamps, you create a secure barrier that holds the hoses firmly, reducing the risk of accidental disconnection or leakage.
Ethanol-resistant hoses are another crucial component when dealing with fuel systems. Ethanol, a common component in modern fuels, has the potential to degrade standard rubber hoses over time. This degradation can lead to hose damage, leaks, and even engine problems. By choosing ethanol-resistant hoses, you ensure compatibility with modern fuels and prolong the lifespan of your fuel system components.
Additionally, when routing the hoses, it is recommended to avoid directing them into the airbox or above the engine. This precaution is especially important for dirt bikes, as fuel leaks near the engine can increase the risk of fires. Instead, consider routing the hoses down behind the motor or back into the system to minimise the potential for leaks and subsequent engine damage.
Finally, when purchasing clamps and hoses, opt for high-quality components that are specifically designed for fuel systems. This ensures their compatibility and durability, reducing the likelihood of failures or leaks.
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Jet sizes: Keihin refers to metering orifice diameter, Amal to flow rate
Jet sizes for Keihin and Amal carburettors are labelled differently. Keihin jet sizes refer to the metering orifice diameter, expressed in millimetres. For instance, a 100 main jet is 1.00mm in diameter, while a 120 main is 1.2mm. On the other hand, Amal jet numbers represent the flow rate, expressed in cubic centimetres of fuel per minute. A 150 jet, for example, will pass 150cc/min.
There is a correlation between Amal and Keihin jets for slow-speed jets. However, the Amal and Keihin carburettors have different air flow rates, so the main jets are not directly comparable. For example, a Triumph 650 Bonneville typically uses an Amal 200 jet, which is comparable to a 122 Keihin in terms of fuel flow. However, a Keihin 130 main jet is usually used for a Triumph Bonneville, which is similar to a 230 Amal jet.
It is important to note that there is no accurate way to match flow rates between different manufacturers. For instance, a Mikuni carburettor with a size 100 main jet would be equivalent to a 110 jet in a Keihin carburettor. While charts can provide a starting point for carb swapping, there are many variables, such as different carb flow characteristics and orifice sizes, that make an exact match impossible.
When adjusting the jetting on a carburettor, it is generally safer to start with a size that is too big and work down. Pilot jets are easier to predict because the vacuum signal is similar across all sizes of carburettors at low throttle openings. However, predicting the main jets can be much more challenging, especially with larger carburettors.
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Removal of the slow-speed jet requires a flat-blade screwdriver
When removing the slow-speed jet of a Keihin PWK Carb, it is important to have the right tools and to follow the correct procedure to avoid damage. The first step is to disconnect the battery to ensure no sparks occur around gasoline vapors. Gasoline is highly flammable, so it is crucial to work in a well-ventilated area or, ideally, outdoors.
The slow-speed jet can be removed using a flat-blade screwdriver. It is important to use a screwdriver that is large enough to fill the slot in the jet. If the screwdriver is too small, it can damage the jet, resulting in the added difficulty of removing a broken jet. Applying a small amount of WD40 around the jet can help loosen stubborn threads and make removal easier.
The jet needle is a critical component in determining the carburetor's jetting. Its three main functions—diameter, length, and taper—have a significant impact on the carburetor's performance. The needle diameter controls the jetting just above the pilot jet as the engine begins to pull. The length of the needle is determined by the clip position, with the top clip position being the leanest setting and the bottom position being the richest.
The pilot jet, located inside the float bowl next to the needle jet/main jet, meters the fuel required for engine starting, idling, and initial throttle response. Proper adjustment of the air screw, a small slotted brass screw on the inlet side of the carburetor, is crucial for fine-tuning the slow-speed system. If no RPM fluctuation is observed during adjustment, it may indicate a clog in the pilot/slow-speed system, requiring thorough cleaning.
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Frequently asked questions
It is recommended to always use clamps on fuel hoses and ethanol-resistant hoses. A 12-inch piece of fuel line and a hose clamp are included with each carburetor. Additional hose and fittings can be supplied if needed.
For Keihin carbs, the jet sizes refer to the metering orifice diameter, expressed in millimeters. For example, a 100 main jet is 1.00mm in diameter. There is no direct crossover with Amal jets, but there is a correlation for slow-speed jets.
To remove the slow-speed jet, use a flat-blade screwdriver that is large enough to fill the slot in the jet. Applying WD40 around the jet beforehand can help loosen stubborn threads.
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