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Motorcycle fuel pump priming occurs as soon as you turn your ignition key switch on. Priming is the process where the fuel pump prepares to build pressure in the fuel system to deliver fuel to the injector or carburetor and start the motorcycle.
So why the motorcycle fuel pump is not priming? The motorcycle pump doesn’t prime due to issues with its parts like the relay, fuse, wires, or motor. Certain sensors on motorcycles assist in priming the fuel pump motor. Through a proper diagnosis, you can pinpoint the problematic components of the fuel pump.
It can be difficult to pinpoint what is really causing the pump to not prime, but following a proper procedure can save you a lot of time.
In this article, you will know why the motorcycle fuel pump is not priming, what are the common causes behind it, and how to fix this problem and get your motorcycle’s fuel pump in proper working condition.
Why Your Motorcycle Fuel Pump Is Not Priming
The basic mechanism of the fuel pump is to prime (getting ready/setting it up) the fuel system by pressurizing the fuel injector or carburetors for some old motorcycles with fuel.
The fuel pump priming process is automatically done by your motorcycle. It’s the buzzing sound your motorcycle creates right at the start when you turn your motorcycle’s ignition key.
This priming process brings the pressure high enough to get rid of some trapped air in the fuel system and fill it with fuel to get the motorcycle engine to start and run properly.
So if there is not enough high-pressure build-up of fuel in the fuel system, the motorcycle fuel pump will not prime.
Reasons Why Motorcycle Fuel Pump Doesn’t Prime?
If the fuel pump isn’t priming, there could be several reasons, and each reason is addressed individually in full detail with brief information on how to fix each problem.
Here Is The List Of Reasons For A Fuel Pump To Not Prime.
- Faulty Fuel Pump Relay.
- Short Circuited Fuse.
- Damaged Power Supply Wires/Plug/Connectors.
- Defective Fuel Pressure Regulator.
- Bad Fuel Pump Motor.
1: Fuel Pump Will Not Prime Because Of Faulty Fuel Pump Relay
The fuel pump relay plays an integral part in supplying the needed voltage/current to the fuel pump for it to function.
When you turn the ignition key on, the fuel pump relay will send a small amount of voltage to the fuel pump for it to prime and create a successful combustion.
The fuel pump relay is located inside or around the fuse box of your motorcycle. The relay can go bad due to increased voltage ( electrical power surge ) to the fuel pump relay causing it to short circuit.
Keep the connecting plug region clean from dust, water, or any kind of contamination.
The relay contacts (prongs) can get eroded due to coming in contact with water or wet moisture.
How To Fix: Once the fuel pump relay is short-circuited you have only one option, replace it with the new relay. Fuel pump relays come at cheap prices typically ranging around 20$- 50$.
2: The Fuel Pump Will Not Prime Because Of Short Circuited Fuse
This one is plain and simple, you should know that fuses absorb excessive electrical power surges to protect the electrical components in the motorcycle.
The electrical system of the motorcycle, which helps the motorcycle to start and run depends on a good functioning fuse. A blown or short-circuited fuse will not the bike start which also results in the fuel pump not priming.
You can refer to the owner’s manual to look for fuses that control the ignition and fuel pump of the motorcycle. If the fusible element is broken which is a metal strip inside the fuse, the motorcycle will not start and the pump will not prime.
Fuses are transparent, so it will be a quick visual check. Also, check the fuse pins to see if they are intact or broken/bent.
How To Fix: If the metal strip inside the fuse is broken that means it’s short-circuited. You have no option but to replace it with a new fuse and check for the ampere range of a fuse that is about to be replaced to install it correctly.
3: The Fuel Pump Will Not Prime Due To Damaged Power Supply Wires/Plug/Connectors
Damage to the wires or plugs or connector pins of the motorcycle can happen over time. If you had bought an old 2nd hand motorcycle, this kind of problem can occur.
You have to look at the electrical system’s wire harness of the motorcycle. It’s not easy to spot the damaged/burned wires because they are covered up by some kind of plastic covering ( typically black in color ).
Sometimes the wires connecting under the fuse box are broken or the female connector’s wiring is burned, shorted, or broken.
You have to also look at the fuel pump’s power supply line or plug to check for any kind of damage as it can lead to the fuel pump not priming.
The fuel pump assembly has two wire connector slots that power the pump and the fuel level sensor, sometimes the wire connecting to these slots/pins are damaged or probably has a loose connection.
You can do the testing of the connector pins or slots using a multimeter and see if they are showing a recommended voltage/ohms. Refer to the owner’s manual or seek a professional mechanic’s help.
How To Fix: Damaged, broken, or burned wires can be replaced or repaired by a good mechanic. For the pins/prongs or sockets, it can be repaired to some extent but it’s better to replace them.
If the connector pins/slots on the fuel pump assembly are damaged, then you might have to replace the whole assembly. Don’t confuse it with a fuel pump motor as the fuel pump assembly hugs the motor.
4: The Fuel Pump Will Not Prime Due To Defective Fuel Pressure Regulator
The fuel pressure regulator controls the pressure of fuel supplied to the fuel injectors and carburetor in the motorcycle.
For a motorcycle fuel pump to prime properly and to run in an efficient way the pressure of the fuel has to be regulated to a certain extent.
A bad fuel pump regulator will have a crack in its diaphragm or the supporting pressure sensor might have failed to cause the fuel pump, not to prime.
How To Fix: You can either disassemble the pressure regulator from the motorcycle and look for a cracked diaphragm and replace it if available. I recommend you guys let the professional handle it for you.
The fuel pressure regulator is usually located under the fuel tank and to see if it’s gone bad, there’s a quick way to find out.
Remove your fuel tank completely or partially then detach the vacuum line from the manifold.
Start the motorcycle and see if the fuel pressure regulator is leaking from the intake manifold pressure intake (that’s where the vacuum line connects ).
A good fuel pressure should not leak fuel from the manifold as it can go into the vacuum line.
If the sensor is gone bad, replace it with the whole pressure assembly.
5: The Fuel Pump Will Not Prime Because Of Bad Fuel Pump Motor
For a motorcycle to run properly and prime successfully every time, it needs a good fuel pump motor.
A bad fuel pump motor can create multiple problems in your motorcycle. And I have already written an in-depth article on the bad/failing fuel pump and what you should look for. Click Here To Read: Top 10 Symptoms Of Bad Or Failing Fuel Pump In Motorcycle
So it’s plain and simple if the fuel pump motor fails it won’t be able to prime. Look out for any kind of corrosion build-up on the motor.
How To Fix: You just have to replace the bad fuel pump if it’s significantly damaged, but try to repair it first by a trusted professional who can give you advice on whether to replace or repair it.
Now you know all the common causes for a motorcycle fuel pump to not prime.
How Do I Know If My Fuel Pump Is Priming?
To understand and know whether the fuel pump is priming or not is pretty simple as you will get audible feedback of its priming process
Once you turn your ignition key “ON” you will hear a low humming buzzing sound from underneath your fuel tank for about 2 seconds. This simply means the motor is priming itself to start the motorcycle.
If you don’t hear any sound during the ignition process, then the motor is not priming itself. This will result in the motorcycle not starting.
How To Fix Motorcycle Fuel Pump & Prime It?
Fixing the motorcycle fuel pump to make it prime involves cleaning the fuel pump strainer and ensuring the power supply connectors are in good condition.
If the parts of the fuel pump such as the pump relay, fuses, or the fuel pump motor are severely corroded or worn then replacement of these damaged parts is necessary.
Priming the motorcycle is a very simple process as it’s done automatically by your motorcycle if your fuel pump is in perfect working condition.
To prime the fuel pump/fuel system of a motorcycle, first, fill the fuel tank with an adequate amount of gas/fuel then switch the engine killswitch to start open and turn the ignition key to on position. This will prime the motorcycle fuel pump properly.
If your motorcycle fuel tank has been completely dry for a few days then repeat the same process mentioned above.
However, the process of turning the motorcycle on and off should be done a couple of times (3-4 times) to get the motorcycle’s fuel pump or fuel system sufficiently pressurized with fuel/gas.
Conclusion
Fuel pumps stop priming the majority of the time due to faults in the fuel supply or power supply systems of the motorcycle. Some motorcycle sensors like the bank angle sensor of the Honda CBR line-up (higher cc) are notorious for going bad causing the fuel pump to stop priming.
