Sylvie Willis
If you're experiencing issues with your Mikuni fuel pump, you're not alone. Many users have reported challenges with finding the right rebuild kits for their specific pump models, as there seems to be a lack of specificity in the available information. It's important to note that oil can potentially plug up the diaphragms of your fuel pump, leading to performance issues. This can happen if your engine is running rich, resulting in a slow burn of the fuel-oil mixture and leaving behind oil residue. To address this, you may need to inspect the pulse line, replace spark plugs, or even consider purchasing a rebuild kit to take a closer look at the internal components of your pump. Additionally, it's recommended to clean any oil residue from the bottom end of the pump to prevent future clogs.
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What You'll Learn
Oil can plug the pulse line that actuates the fuel pump
To check if your pulse line is plugged with oil, pull the pulse line off the fuel pump and pull the recoil a couple of times. Look to see if fuel/oil comes out of the pulse port on the crankcase. Make sure your spark plugs are in when you do this, and if they are black and wet, you should replace them.
If your pulse line is plugged with oil, you can try to clear it by removing the crank plug and running the engine to burn the excess oil. Alternatively, you can remove the head and jug from the base and sit the sled on its side for an hour or so to allow the oil to drain. You can also try using a fuel injection cleaner in your fuel mixture to help remove the oil.
To prevent oil from plugging the pulse line in the future, it is recommended to mount the fuel pump higher, on top of the engine. This allows any oil that does get into the line to drain back into the crankcase instead of into the fuel pump.
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The pump should be mounted above the engine pulse source
It is recommended that the Mikuni fuel pump is mounted above the engine pulse source. This is to allow any fuel that enters the pump from the pulse line to drain out. If the pump is not mounted above the engine pulse source, the fuel will not be able to drain and can cause the pump to lock up.
The pump should be mounted as close to the pulse port as possible without letting the pump get hot. It should be mounted horizontally, with the weep hole facing downward to allow for the drainage of any fluid build-up. The weep hole in the pump body should be small and face downward. This is another reason why the pump should be mounted above the engine pulse source, as any fluid or fuel build-up can drain out through the weep hole.
The pulse line should be stiff to improve the performance of the pump. It is also important to ensure that the oil is cleaned from the bottom end as it can plug up the new pump. One way to do this is to remove the crank plug if it is an older motor. Another way is to run the engine all day to burn off the excess oil or to remove the head and jug from the base and sit the sled on its side for an hour or so.
Additionally, it is possible for oil to plug up the diaphragms of the gas pump, but this is not through the fuel line. A rich fuel/oil mix will burn slowly, leaving a little oil that can build up in the bottom end of the motor and enter the pulse line. To check for this, the pulse line can be removed from the fuel pump, and the recoil can be pulled a few times to see if fuel/oil comes out of the pulse port on the crankcase. If the spark plugs are black and wet, they should be replaced.
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The pump should be mounted horizontally
Mikuni fuel pumps are commonly used in Ski-Doo snowmobiles. It is possible for oil to plug up the diaphragms of a gas pump, and this can happen if you are running too rich, causing a fuel/oil mix to burn slowly and leave oil residue. This can then enter the pulse line and cause a blockage.
To avoid this, it is recommended that the pump is mounted horizontally, with the drain hole at the bottom, pointing downwards. This is because any water or fuel that accumulates in the diaphragm area can then drain to the crankcase. If the pump is mounted vertically, with the drain hole pointing upwards, the pump could eventually become half-filled with liquid or vapour that has condensed in the line. This can compromise the pressure achieved at the carbs and cause excessive EGTs.
The pump should be mounted as close to the pulse port as possible, without letting the pump get too hot. It is also important to use a stiff pulse line. The pump body should have a very small weep hole to get rid of any fluid build-up, and this should face downward, which is why the pump should be mounted horizontally.
If you are concerned about oil in the fuel pump, you can buy a rebuild kit for a small cost and take the pump apart to inspect it.
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$62.95 $67.52
The pump body should have a small weep hole to get rid of fluid build-up
Weep holes are commonly found in water pumps and are designed to allow the drainage of excess fluid. In the context of water pumps, the weep hole is located between the oil and coolant seals. If the oil seals are leaking, the weep hole allows the extra lubricant from the pump bearings to drip out of the housing, preventing it from mixing with the coolant. Conversely, if the coolant seal is leaking, the weep hole enables the coolant to escape, preventing it from contaminating the oil bearings.
In the case of a Mikuni fuel pump, the weep hole serves a similar purpose. By providing a drainage point, the weep hole helps to prevent the build-up of excess oil or fuel. This is particularly important as oil build-up can occur in the bottom end of the motor and enter the pulse line, potentially affecting the fuel pump's performance.
Additionally, the presence of a weep hole allows for early detection of seal failures. If oil is observed leaking from the weep hole, it indicates a blown or failing oil seal. Similarly, if coolant or antifreeze is leaking from the weep hole, it signifies a leaking internal water pump seal. Therefore, the weep hole serves as an early warning system, enabling proactive maintenance and preventing more severe issues from occurring.
Overall, the inclusion of a small weep hole in the pump body is essential for proper fluid management and the prevention of contamination. It also serves as a diagnostic tool, providing visual indications of potential seal failures, allowing for timely interventions to ensure the optimal performance of the fuel pump.
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Fuel pump rebuild kits are available for round-style Mikuni fuel pumps
The fuel pump rebuild kits for round-style Mikuni fuel pumps typically include all the necessary components to revitalise the internal workings of your pump. These kits are designed for the specific dimensions and requirements of Mikuni pumps, ensuring a precise fit and seamless integration. Within the kit, you'll find replacement parts crafted from high-quality materials, meeting or even exceeding the specifications of the original equipment.
The inclusion of components may vary slightly depending on the kit, but generally, you can expect to find items such as diaphragms, check valves, O-rings, gaskets, and other necessary seals. These parts are crucial for maintaining the pump's pressure, preventing leaks, and ensuring the smooth flow of fuel. By replacing these components, you're effectively restoring the pump's functionality, enhancing its performance, and extending its lifespan.
Installing the rebuild kit is a relatively straightforward process, but it requires careful attention to detail. It is essential to follow the instructions provided with the kit and consult a repair manual specific to your Mikuni fuel pump. Disassemble the fuel pump, carefully removing the old parts, and thoroughly clean the pump housing and components that will remain.
Once the pump is clean and dry, install the new parts from the kit, handling them with care to avoid damage or contamination. Refer to the instructions for correct placement and orientation. Take your time to ensure the pump's reliability and longevity.
After reassembly, inspect the fuel pump for any signs of damage or misalignment and verify connections are tight and secure. Once satisfied, reinstall the fuel pump according to the guidelines.
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Frequently asked questions
Yes, oil can plug up your Mikuni fuel pump. This can happen if you are running too rich and oil has plugged the pulse line that actuates the fuel pump.
Pull the pulse line off the fuel pump and pull the recoil a couple of times, looking to see if fuel/oil comes out of the pulse port on the crankcase. Make sure your spark plugs are in when you do this, and if they are black and wet, you should replace them.
It is recommended to mount the pump above the engine pulse source to allow any fuel that may enter the pump from the pulse line to drain out. The pump should also be mounted horizontally, with the body having a very small weep hole to get rid of any fluid build-up.
You can buy a rebuild kit for around $10 and take it apart to clean it. Alternatively, you can try to burn the excess oil by getting the engine going all day to get it nice and hot.
