How to change generator spark plug: A step-by-step guide

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    Is this the time of year when you need to replace your worn-out spark plugs and tune up your generator?

    Although it looks complicated, the actual replacement procedure is very simple. For a skilled handyman, this will be a breeze.

    With the help of BISON’s guide and the instructions in the user manual, hobbyists won’t have any problems either.

    Our first recommendation is to read the manual carefully before starting the replacement process, which contains information on the correct spark plug type.

    Find the brand, model, required size, and gap

    Obviously, during the replacement process, if the instructions are not followed correctly, a lot of damage to the engine can be done.

    This is why you should realistically assess your skills. If you feel like you can’t do all the steps, it’s wise to spend the extra money to have the old spark plugs replaced by a professional.

    So let us guide you through the process of changing the generator’s spark plug.

    What are the benefits of changing spark plugs?

    The main benefit is knowing your generator will start smoothly. It goes without saying that this is not the most crucial factor. The new spark plugs also offer many other performance benefits:

    a) Continue to produce optimal combustion

    Fully functional spark plugs help support a fully functional combustion system. Run this successfully, and many of your performance issues may become a distant memory.

    b) Better fuel economy

    Spark plug misfires can reduce fuel efficiency by 30 percent. Replacing new plugs at specified intervals can help maximize fuel economy and save you money.

    c) A smooth and dynamic start

    Turning the ignition with a new spark plug for the first time can be an eye-opener. The old can be the reason your generator is experiencing those jerky starts.

    d) Reduce harmful emissions

    Diligent generator maintenance—especially spark plugs—can help improve fuel efficiency and reduce air pollution.

    A step-by-step guide to changing generator spark plug

    Before you start changing plugs, you need to ensure the generator’s power switch is in the off position and all power cords are unplugged.

    Also, if you have run the machine before you decide to replace the spark plug, ensure its surface isn’t too hot, as you can easily burn your skin.

    That’s why we recommend wearing some protective gloves and glasses.

    Once this is done, you can move on to these steps.

    Step 1: Find the spark plug

    Finding the spark plug’s location is the first and frequently most difficult step, especially if you’re doing this for the first time. Usually, it’s hidden under a removable housing and covered by a spark plug cover.

    The easiest way to find the spark plug is to find and follow a black cable that goes to the engine with a boot on the end, similar to the picture below.

    Check the owner’s manual if you are having trouble positioning the spark plug. It might provide clues as to where it might be hiding and how to approach it most effectively. Additionally, some brands and more potent models might have multiple spark plugs.

    This is why you should always check your generator’s instruction manual.

    Step 2: Disconnect the plug cord

    Once you’ve found where the old plug is, you’ll need to remove the wires attached to it. To do this safely, you need access to the spark plug wire guide.

    Once you have good access, hold the boot firmly, twist in either direction, and pull out simultaneously.

    This way, you can easily disconnect the wires even if they are slightly corroded. The rotational motion helps loosen the connection from the spark plug, reducing strain on the wire.

    Never pull on the wire section, as this can easily damage it.

    Step 3: Clean everything around

    After unplugging the cord, you need to ensure that the old plug and everything around it is clean. Take the time to do this, as you could seriously damage your generator if you neglect the cleaning process.

    Once unplugged, you will have an opening directly into the engine. Anything that enters it will eventually cause damage.

    So be sure to remove and clean any dirt, debris, and oil residue that may have fallen in.

    Step 4: Unplug the old plug

    If everything is clean and you’re sure nothing could fall into your engine, you can go ahead and remove the old plug. A ratchet and the appropriate spark plug socket are required.

    Just check the instruction manual that came with your generator. Information should be posted there. Once you get the correct socket, you need to connect it to the spark plug by hand.

    You can install the ratchet if it is properly seated on the spark plug.

    Add extensions if needed.

    Just use the ratchet to loosen the spark plug and then remove it. Do the rest of the threading/unscrewing by turning the socket by hand.

    When disassembling, do not change the angle of the socket; otherwise, the plug will be damaged.

    Once unplugged, remove the plug from the outlet to make room for the new plug.

    Step 5: Inspect new spark plugs

    Before putting new spark plugs in the generator, make sure you have the correct model, size, and clearance. For this, use the gap measurement tool. It’s not expensive, and it’s convenient.

    With this tool, you can measure the gap between the two electrodes (one straight and one curved) at the tip of a new spark plug.

    You can do this by putting a feeler gauge into the gap until you can still move it freely but start to feel a small amount of resistance.

    It should not be too loose nor too tight.

    When you have finished measuring, compare it to the manual one. If it’s the same number, then feel free to go to the next step.

    If you’re still unsure if your plug is correct, consult a professional at your local hardware store.

    They will be happy to help you.

    Step 6: Install a new plug

    Once you have the correct clearance on your plug, you can install it. Just grab the empty spark plug socket, insert the new plug into it, and put it into the empty socket in the engine.

    You can wiggle it a little until it sits properly in the hole, then gently rotate it with your hands.

    It should go smoothly without any resistance.

    At this point, it’s easy to get through the plug, so use it gently, and if it resists, remove it and try reinstalling again.

    If it doesn’t give you resistance, keep turning it manually until you can’t turn it anymore.

    Then, connect the ratchet to the socket and tighten the spark plug. Be careful not to overdo it. Usually, 1/4 turn is enough, but this number may vary, so it’s better to see your instruction manual.

    Once tightened, you can remove the ratchet and spark plug sockets.

    Step 7: Reconnect the plug cord

    Once the new spark plug is securely in place, you will need to reconnect the wires. Again, grab the sheath of the spark plug wire and slide it over the top of the plug. Then, press it until it’s fully in.

    Typically, you will feel or even hear the connector click into the correct position. After reconnecting the plug, you can reinstall any covers you had to remove, and you’re good to go.

    Don’t forget to give it a test run to see if everything works well.


    Now that you have the knowledge on how to change the generator spark plug, you can do it whenever you need to. Check the manufacturer’s manual for advice on the type of spark plug you need and how often you need to change it.

    When it’s time to change the spark plug for your generator, you can rely on BISON to guide you. We invite you to contact us at (+86) 17380831819 for more information on changing spark plugs and our generator maintenance program.

    Spark plugs should be replaced approximately every 100 hours of use. Spark plugs should also be checked during generator repairs and maintenance to ensure they are not worn or cracked.

    The vast majority of portable generators require spark plugs with a clearance size of 0.028" - 0.031" (0.7mm - 0.8mm).

    Spark plugs depreciate over time, so if you don’t replace them, you can have engine problems. When the spark plug does not produce enough spark, the combustion of the air/fuel mixture becomes incomplete, resulting in a loss of engine power, and, in the worst case, the engine will not run.

    Torque specifications for spark plugs are for cold engine conditions. Installing the spark plug while the engine is hot can change the torque specification and how the threads on the engine and spark plug interact. Depending on the application, this can cause the plug to be too loose or too tight.

    Symptoms of spark plug misfires include uneven power under acceleration, rough idling, and increased exhaust emissions.

    The National Institute for Automotive Service Excellence states that poor-quality spark plugs can reduce fuel economy by up to 30 percent and can cost as much as 94 cents per gallon at current prices.

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