If your pressure washer pops after squeezing the trigger, there…it just backfired!

While that sound isn’t encouraging to any user, especially during a house chore, it is a common problem with pressure washers.

But why is your pressure washer backfiring?

For several reasons! But the most likely culprits are rogue spark plugs, carburetors, or fuel mixtures.

However, the good news is that they are all fixable; you just have to know what to look for.

Let me show you!

Why Is My Pressure Washer Backfiring (7 Key Reasons)

Things to hold accountable if your pressure washer keeps backfiring are:

7. Bad Engine Timing

Bad timing in engine combustion occurs when the fuel-air-heat ratio is disrupted.

Without proper timing control, excess fuel can enter the exhaust pipe. And when exposed to air and heat, this fuel may combust outside the chamber, resulting in a loud boom and potential fire hazard.

Precise timing is crucial for safe and efficient engine operation —even though it is slightly out of your control.

6. Lean Fuel Mixture

A lean fuel mixture means there is not enough fuel in the air-fuel mixture being combusted in the engine.

This happens when the carburetor or fuel injectors are not supplying enough fuel. So, when there is excess air and insufficient fuel, the combustion process becomes unstable, leading to a backfire.

5. Rich Fuel

On the other hand, a rich fuel mixture means there is too much fuel in the air-fuel mixture. This can occur if the carburetor or fuel injectors deliver too much fuel.

When the amount of fuel is much, it can ignite and explode in the exhaust system, causing a backfire.

4. Old Engines

Over time, engine components can wear out or become damaged, affecting their performance.

Parts such as valves, spark plugs, or the ignition system may deteriorate in older engines. This can disrupt the proper ignition of the fuel-air mixture, resulting in backfiring.

Worn-out components may also lead to fuel delivery or combustion timing issues, further increasing the problem.

3. Muffler Construction

While the muffler itself does not directly cause backfiring, its design and construction can impact how the sound of the backfire is suppressed.

A poorly designed or malfunctioning muffler may not effectively dampen or redirect the sound, making the backfire more noticeable to the user.

However, the root cause of the backfire lies elsewhere in the engine system.

2. Lowering Engine Speed Quickly

Abruptly decreasing the engine speed while the throttle is open can rapidly change the engine’s pressure. This sudden pressure change can disrupt combustion, leading to a backfire.

The fuel-air mixture may ignite prematurely due to the rapid decrease in engine speed, causing combustion to occur at the wrong time and resulting in a backfire.

1. The Temperature In The Engine Is Too High

When the temperature in the engine becomes too high, it can lead to issues such as pre-ignition.

Pre-ignition occurs when the fuel ignites before the spark plug fires, while detonation refers to the uncontrolled explosion of the air-fuel mixture. Both can cause backfiring as the combustion occurs at the wrong time.

High engine temperature can result from insufficient cooling, malfunctioning cooling systems, or prolonged heavy usage.

Solution To Backfiring Of The Pressure Washer

We’ve discussed potential issues and their underlying causes, but your ability to manage and resolve them is what matters.

Turning off your engine gradually rather than abruptly is best to prevent backfiring.

Changing to a fuel brand with less alcohol could also be beneficial. You can also consider tuning or adjusting your engine to ensure ideal timing.

If you keep having problems, the airflow sensor or the air filter might be to blame. Consider both of these factors and get professional advice.

Frequently Asked Question

How Do I Properly Store My Pressure Washer?

You must first run your pressure washer’s motor dry and drain the gas before storing it properly.

Antifreeze ought to be pumped through the pump and kept there. Doing this can prevent the pump from freezing and internal corrosion brought on by water.

Additionally, it lubricates and prevents the seals from drying out, enabling instantaneous use. All hoses should be disconnected from the machine, cleaned, and any liquids removed.

Finally, keep your pressure washer somewhere cool and dry.

Why Doesn’t My Pressure Washer Reach Full Pressure?

There are several possible causes for why your pressure washer may not be using all of its pressure.

Worn-out packings are one potential factor, as they can reduce the pump’s efficiency and the seal around its openings.

Furthermore, a blocked inlet water valve or a clogged filter may be responsible for the machine’s insufficient water supply.

Also, a kink in the hose may prevent water from flowing and lower pressure output.

Does A Backfire Damage An Engine?

Backfires can be alarming, but they typically don’t harm modern engines much. A backfire typically indicates a problem with the engine’s air-to-fuel ratio or ignition timing.

If a backfire explodes with a lot of force or happens frequently, it may occasionally harm sensors, the exhaust system, or other parts of the engine.

However, modern engines are built to withstand occasional backfires without significant damage.

Can I Use Hot Water With My Pressure Washer?

Depending on your pressure washer, using hot water with a pressure washer can be helpful for some cleaning tasks.

Therefore, using hot water is completely acceptable and can even increase the cleaning effectiveness for some applications if you have a pressure washer explicitly made for use with hot water.

However, it’s essential to adhere to the instructions and suggestions provided by the manufacturer for using hot water with your specific pressure washer model.


As much as the question expresses deep frustration and confusion, I can understand the headache it brings because I’ve been there before.

But it is imperative to understand the reasons behind this issue to find practical solutions.

As mentioned earlier, we recommend examining the fuel mixture, inspecting the spark plug for any damage, cleaning or replacing the air filter, and checking for mechanical problems.

But if things get out of hand, call a professional mechanic. 

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