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Why does my pressure washer idle up and down? Helpful tips

You may notice that when the pressure washer revs up and down during the idle stage, it produces a loud noise while going dead at other times. A pressure washer idling up and down is not a sign that you have a major issue. Most causes are easy to fix without a lot of experience.

Why does my pressure washer idle up and down:

In general, a pressure washer idles up and down due to a jammed unloader valve, a restricted carburetor, degraded fuel, or blockage in the air or fuel filters. A clogged carburetor will not mix the correct air-fuel mixture for the engine. A faulty or jammed unloader valve exerts an additional load on the engine and does not release the high-pressure flow. This causes the engine to idle up and down. Clogged air filters and degraded fuel also cause a pressure washer to idle up and down.

This article will provide you with information and tips to help you troubleshoot and fix most of these problems. I will also show the causes of erratic pressure.

The top 5 reasons for a pressure washer to idle up and down

The top 5 reasons for your pressure washer to idle up and down are:

● Reason 1: Restricted Carburetor

A clogged carburetor is one of the most common reasons for an engine to be experiencing idling problems. It supplies the air-fuel mixture to the engine. Bad gas, dust build-up, and poor maintenance can restrict the carburetor’s jet. Due to these blockages, the wrong air-fuel mixture in the engine can cause it to produce noises or even stop completely.

Residue from bad gas being left in the tank can create a sticky residue in the carburetor. Fuel in the tank must be refreshed regularly. When it is older than a month or two, parts of the gas will evaporate, leaving some sticky residue. This happens especially when you have not used your machine for some time, like during the winter. I recommend draining the fuel before this period. And use fresh fuel when you want to use it again. Another solution is to add some fuel stabilizer to the tank. Do not forget to add it to other stored gas as well.

To clean the carburetor, disassemble it. Clean the carburetor and the jet with some carburetor cleaner. Ensure that all the sticky residue is removed.

If cleaning the carburetor is not effective, use a carburetor repair kit to replace some of the components or install a new carburetor altogether.

A pressure washer engine can also idle up and down due to loose screws in the carburetor. Check that all are correctly tightened.

● Reason 2: Clogged Fuel Filter

Old, bad gas can also create a clog in the fuel filter. This can also cause the pressure washer to idle up and down. I recommend replacing the clogged fuel filter with a new one.

● Reason 3: Clogged Fuel Cap

As fuel is consumed, the level in the fuel tank lowers. To make up for this, fuel caps have small vent holes to allow air into the tank. If the vent holes are blocked, air will not be able to enter the tank. This creates a vacuum that can cause the engine to run rough or even stop.

You can test this by starting the engine without a fuel cap. If it is idling fine, there is a problem with the fuel gap. You can either clean the clogged vent holes. Or replace the fuel cap with a new one.

● Reason 4: Dirty Air Filter

A dirty air filter can cause a pressure washer to idle up and down. It will restrict the air coming into the carburetor and not allow the machine to run correctly.

To fix the, remove the air filter. Check if it is dirty. If it looks damaged, replace it. If your machine uses a paper air filter, you have to replace it as well. A foam filter can be cleaned with some warm water. Let it dry completely before mounting it back.

Check an air filter regularly. It should be part of your maintenance routine. Expect to replace an air filter annually or when it is really dirty. 

● Reason 5: Problem with the Spark Plug

A pressure washer may idle up and down due to a problem with the spark plug. Examine the spark plug wires and tighten them if loose. Check for any corrosion or build-up of deposits at the edge of the plug. You can remove it by using a metal brush. If the spark plug does not look fine, replace it.

How to fix a pressure washer idle up and down?

To fix the problem of idling, you need to clean the pressure washer’s carburetor. Check and replace a faulty unloader valve. Use fresh gas, and clean or replace the air filter.

● Pressure washer idle up and down: Clean the carburetor

Use the following steps to clean the carburetor:

– Step 1: Unscrew the front casing:

First, you need to unscrew the front cover to get access to the carburetor.

– Step 2: Detach the gas lines:

Detach the fuel lines leading to the carburetor. Drain the gas, or carefully remove the clamps to avoid any gas leakage. I recommend draining the gas if it is more than a few months old.

– Step 3: Remove the carburetor:

After unscrewing and detaching the fuel lines, remove the carburetor. Make some images or a small video of the process. You can use that later when assembling the carburetor.

– Step 4: Examine the jets and screws:

Check the jets and the rest of the carburetor. For unclogging and cleaning, use a carburetor cleaner liquid or spray.

– Step 5: Reassemble:

Once you have cleaned the carburetor, you need to reassemble the carburetor. Start the engine and check if it solved the idling problem.

● Pressure washer idle up and down: Inspect and replace the unloader valve

A problem with the unloader valve can be the reseason for your idling problem. To check the unloader valve, you have to disassemble it partly. You will need to unscrew and remove the external casing of the pressure washer to see the pump. Once the pump is visible, you may see a valve with a spring-loaded plunger below the outlet valve. This is the unloader valve.

Adjusting the unloader pressure valve is a tricky process. The goal of the unloader valve adjustment is to find the spot where the pressure is maximum. And the pressure spike when you release the trigger is minimal. Remove the top, lock the nuts. Clip the pressure gauge and start tightening the spring. Once the spring is adjusted, engage the trigger to prevent blockages in the unloader valve. Adjust the knob until you find the spot where pressure is maximal, and the spike is minimal.

The unloader valve of a pressure washer has a tension spring which is responsible for releasing the pressurized water when the trigger is pressed. The tension spring is also responsible for decreasing the pressure when the trigger is released. By adjusting the pressure washer unloader valve, the goal is to find the ideal setting for the tension spring.

Always ensure that the pressure spike that you will see when you release the trigger is less than 10%. A higher spike can damage the pressure washer.

● Pressure washer idle up and down: Add fresh fuel to the tank

Carburetor’s jets get clogged due to bad gas. For gas-powered pressure washers, fuel should not be left in the tank for more than a month. If it is older and you have problems, drain it from the tank and the carburetor. Check the carburetor for any sticky residue. Remove it with some carburetor cleaner. The last step is to add some fresh gas. If you plan to store your pressure washer for more than a month, add some fuel stabilizer to the tank and other stored gas.

● Pressure washer idle up and down: Clean the air filter

The air filter in a pressure washer filters the dust particles in the air. A pressure washer idling up and down can be due to an inadequate supply of clean air. This can be due to a dirty air filter.

Use the following steps to clean your air filter:

– Step 1: Open the air filter lid

Open the air filter casing located next to the fuel tank and carburetor. Remove the air filter and clean the dust and debris inside the case.

– Step 2: Clean the filter

Suppose your pressure washer is using a foam air filter. Use a mixture of soap and warm water to clean it. If you can not clean it well, or it is damaged. I recommend replacing it. If your machine uses a paper air filter, always replace it.

– Step 3: Check for soap residual

After cleaning the air filter, ensure that there is no soap residue left. Let the filter dry completely.

– Step 4: Apply engine oil

Apply a small amount of engine oil to the filter. This will keep small dust particles from reaching the engine.

● Pressure washer idle up and down: Check the inlet hose and filters

Check the inlet hose and filter for any possible issues. Often they contain some dirt. Clean the hose entirely. If there is any leakage, repair or replace it.

● Pressure washer idle up and down: Check the water supply

Sometimes, the water source you use may not be supplying enough water. Check the amount of water that enters the pressure washer. Most manufacturers mention that a minimum of 2 gallons per minute (GPM) is needed. But my experience is that it will function fine with a lower amount. But expect that it needs at least 0.9 GPM.

If you use a longer hose, I recommend a diameter of ¾ inches. This avoids any surging in your pressure washer. If the washer’s pressure keeps pulsing, even when using a ¾ inch hose. Check for any blockage. Try a shorter hose with the least amount of curves. The longer the hose, the less water pressure there will be at the end.

Erratic Pressure Washer Engine Revving

If your pressure washer experience some erratic engine revving, this can be due to a problem with the air filter, a gas issue, a problem with the spark plug, or an improper carburetor adjustment.

● Erratic Engine Revving: Wrong Carburetor Adjustment

A poorly adjusted pressure-washer carburetor is one of the common causes for the engine to rev erratically. Most pressure washers have one or two screws on the carburetor that can be used to adjust the carburetor.

Start the engine and let it warm to normal operating temperature. Adjust both screws equally and find the right setting. The goal is to have a smooth-running engine.

● Erratic Engine Revving: Gas Issues

When you have gas in your tank that is more than 2 months old, it can be bad gas. It can lead to erratic engine revving. Drain the old gas, and replace it with fresh gas. Check the carburetor, and clean when necessary.

Do not let gas in the tank for two months, or add some fuel stabilizer. Do not forget to add this also to other stored gas.

● Erratic Engine Revving: Problems with the air filter

If your engine is revving erratic, the air filter may be dirty. This may stop enough air from entering the carburetor and lead to sporadic engine revving. Check the air filter and clean it. When the air filter is damaged, or you use a paper air filter. Replace it.

Also, check the hole in the fuel cap. This needs to be open to let air in when the engine is running. To test this, you can run the engine without a fuel cap. If it works fine, the fuel gap hole is the problem. Try to clean it with a thin metal wire.

● Erratic Engine Revving: Spark Plug Issues

If your pressure washer engine revs erratically, there can be a problem with the spark plug. Check that the spark plug wire is connected firmly.

Remove the sparkplug and check if it looks ok. Use a metal brush to clean any deposits. Replace if needed.