How to bypass a solenoid starter on a lawnmower, step by step


One fine morning, you are in a great mood and want to cut the grass off your lawn. You gear up and bring the mower out. After fueling it, you try and start it by turning the ignition switch, but the lawnmower will not respond. It seems as if the battery is dead. This might be the case, but you can check that easily with a battery checker of a multimeter. If the battery is not the problem, some people will suggest you check all of the safety switches. But in case the seat safety switch, the parking brake safety switch, and even the fuel safety are working fine, there could be a problem relating to the ignition system, the sparkplug, or the ignition coil. It is always a good idea to check the oil level as well. Fuel supply can be the reason to. The best way is to diagnose the problem one by one and eliminate the possibilities.  

How to bypass a solenoid starter on a lawnmower, step by step:

The battery is working, but the solenoid is dead

  • Step 1: Turn the ignition switch on the “RUN” position
  • Step 2: Track down the lawnmower solenoid
  • Step 3: Find out the copper posts to be jumped
  • Step 4: Clean the carbon and rust deposits from the terminals
  • Step 5: Jump the solenoid
How to bypass a solenoid starter on a lawnmower, step by step 1

The battery of the lawnmower is also dead

  • Step 1: Arrange a battery and jumper cables
  • Step 2: Notice the fuel solenoid and bypass it if required
  • Step 3: Locate the starter motor
  • Step 4: Keep connecting the wires one by one
  • Step 5: Turn the choke up and ignition switch to “RUN.”
  • Step 6: Touch the negative terminal of the battery

You’ve already been through all the checks, and all main parts, such as spark plugs, ignition coil, carburetor, fuel supply, and lubrication, are working great. However, the mower is still not starting. This condition gives two hints of potential failure. One is a defective starter motor, and the other is a poor or broken solenoid.

Working of the Lawnmower stater circuit. What components are involved, and how to test the solenoid

Involved Lawnmower Components:

  1. Battery: The 12 V source that is installed in the lawnmower. It serves as the primary source of power to operate the accessories, such as a lamp, fan, etc., and cranks up the starter mechanism to start the engine. The 12 V is stepped up to have the capacity for the production of sparks as well.
  2. Solenoid: The electromagnet present after the battery relays the current flow from the battery to the starter engine. Generally speaking, a click sound is heard as the solenoid engages. As soon as the key’s signal is received, the magnet becomes active due to current flow. It creates contact between the motor and battery, and the engine becomes operative.
  3. Starter motor: When we need to power a lawnmower, the motor needs an initial boost to get air and gas to get to the first spark. This operation is done to get the engine started by the motor, geared to the flywheel or the engine’s crankshaft.

Diagnosis:

It can be observed that the lawnmower’s failure to start can be due to several reasons and some malfunctioning components. In short, the solenoid cannot be blamed directly. To be clear whether or not to jump a solenoid, the diagnostic part is important. If you want to be quick and know the reasons, you might want to skip to the step-by-step guide.

  • Check the battery voltage: Using the digital multimeter in the volts setting, check the voltage across the negative and positive terminals. Anything over 12V is good.
  • Check the solenoid continuity: Touch the solenoid positive and ground terminals to a battery pack. Check the continuity using DMM on the main copper posts.
  • Check the starter motor: Look around the engine for any electric spark or blow mark. If the motor winding is intact, the motor is good to use.
  • Check the starter fuse and wires: Using a DMM, check the continuity of the fuse. It is generally a 10 A fuse. The wires’ continuity can also be contained in the same manner.

Jumping/ Bypassing the solenoid Is not only a method to start the lawnmower but also a diagnostic step to confirm the malfunctioning solenoid starter.

How to bypass a solenoid starter on a lawnmower: Step by step

Bypassing the solenoid is a handy method to start a lawnmower with a faulty solenoid quickly. The technique can vary a bit depending upon whether or not the battery works. The purpose of both these methods is to apply the current directly to the starter motor as the solenoid will not engage in doing so.

Equipment Needed

Following materials are required to bypass the solenoid starter.

  • Jumper cable
  • Digital Multimeter (DMM)
  • Emergency Battery pack (12 V)
  • Metal screwdriver
  • Sandpaper/ Wire brush

The battery is working, but the solenoid is dead

Check the battery with a battery tester or a multimeter. If it works fine the system will have a healthy 12V. The continuity of the wires is also set. Make sure to brush away any corrosive dust on the terminals or points of contact.

•Step 1: Turn the ignition switch on the “RUN” position

  • Give the engine a try: Try to start the engine by turning the button to “START.” The machine would take power but sputter and will be unable to start
  • Keep the switch at “RUN”: Put the Ignition key on the “RUN” position. This allows the current from the battery to follow through the circuit.

•Step 2: Track down the lawnmower solenoid

  • Find the battery: First, locate the battery that mostly under the seat
  • Follow the wire: Track the wire from the positive terminal that ends up to a cylindrical structure with either 3 or 4 wires attached to it.
  • This cylindrical component is the starting solenoid.
  • Type of solenoid: The three-pole solenoid has a common ground and is connected to the mower’s body. The four-pole solenoid has a specific terminal for the ground as well. 

•Step 3: Find out the copper posts to be jumped

The solenoid has two terminals that are larger and have very big wires attached to them. One wire leads up to the motor, and the other is from the battery’s positive terminal. These two larger copper posts are our terminals of interest.

•Step 4: Clean the carbon and rust deposits from the terminals

Using a wire brush, clean any dirt or rust from the terminals.

•Step 5: Jump the solenoid

Use a metallic strip, for instance, a screwdriver, to connect the positive terminal from the battery to the motor. This will allow the circuit to get complete and, resultantly, start the lawnmower.

The battery of the lawnmower is also dead

If you check the battery with a battery tester or a multimeter, and the voltage is below 12V, the battery is also faulty.

•Step 1: Arrange a battery and jumper cables

You have two options. Charge the battery. Or use an alternative source that can deliver a constant 12V. In that case, you also need Jumper cables with alligator clips.

•Step 2: Notice the fuel solenoid and bypass it if required

Observe if you have a wire protruding out from the carburetor. This is a safety switch solenoid that hinders the flow of fuel through it. You will have to bypass this solenoid as well using a simple jumper cable.

•Step 3: Locate the starter motor

A starter motor is usually present on the engine’s side and is coupled using gear to crank the engine. The motor has a single positive terminal and is grounded through the body of the lawnmower.

•Step 4: Connect the wires one by one

  • Connect the wire from the positive battery to the positive of the motor.
  • Connect a wire to the body of the lawnmower to act as a ground

•Step 5: Turn the choke up and ignition switch to “RUN.”

  • Choke is also turned up to aloe excessive fuel flow to keep the fuel supply on a richer side.
  • Turn the ignition switch to “RUN.” This will cause the mower to run all safety switches and hold the parking brake.

•Step 6: Touch the negative terminal of the battery

Using the free end of the ground wire connected to the body of the lawnmower first touches the battery’s negative terminal.

This will cause the circuit to complete, and the engine will startup.

Precautions:

  • Keep away from flammable: Try to keeping volatile or fire-catching liquid or gas away from the solenoid. A spark is generally caused, which might be dangerous
  • Open environment: try to perform the procedure in the open air rather than a closed garage or shop
  • Eye protection: For jobs that can be dangerous for your eyes, wear some eye protection.

Related questions

1. What to do if the ignition switch is also not working?

Before attempting to jump the solenoid, make sure the wires “B” and “L” terminal of the switch are joined together. This is the same as putting the switch in the “RUN” position.

2. If the mower starts when the solenoid jumps, what does it indicate?

Suppose you didn’t have made the diagnosis already, and you wanted to save time. Once the solenoid jumps, the mower starts. This indicates that the solenoid does not function properly in the starter circuitry and must be replaced.

Final Remarks

If starting your lawnmower is not possible because the solenoid is faulty. Bypassing is the simplest, most convenient, and time-saving way. The technique is not only a solution to a problem but also acts as a confirmation. Indicating whether the solenoid is causing the failure or not. If the lawnmower does not start this blog post, it will help you fix the problem and start your machine.

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