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Pressure Washer Engine Will Not Idle

You have just woken up on a fine weekend morning, and washing your car is the first thing on your to-do list. On a fine Saturday, you happen to get a phone call right amid your power washing. You see that the engine has shut down as soon as you return, whereas you left it idle. That seems strange to you since it has happened the first time, but you don’t want to visit a mechanic immediately. If you haven’t done maintenance on your machine before and don’t exactly know where to start, there is no need to panic. This article will provide you with all the knowledge you need to fix this issue on your own. Sounds cool, right?

If a pressure washer does not idle, the most probable cause can either be a jammed unloader valve or blockages in the carburetor or filters. Due to these reasons, the engine’s power is either insufficient or runs short of the load exerted on it by the pump. Listed below are the prominent causes of the problem.

Pressure washer engine will not idle, what might be wrong:

  • The clogged carburetor in which blockages inhibit the air-fuel mixture to be drawn in an appropriate amount
  • Faulty unloader valve that does not release the high-pressure flow and exerts an additional load on the engine

Some additional causes include:

  • A clogged air filter that does not provide a clean air-fuel mixture to the engine
  • Degraded fuel quality that causes debris to build up in the components

Now, suppose you aren’t sure how you would locate, change, or clean these components. Or what steps you should be following, and in what order. In that case, you don’t need to worry. We have done the hard part for you by listing all the necessary steps, with a detailed explanation of the procedures that will surely fix your engine idling problem.

Steps To Troubleshoot a Pressure Washer Engine That Will Not Idle:

Idling of a pressure washer is a condition when the engine keeps running, but the pump stays shut, i.e., no pressurized stream of water is used. If an engine shuts down whenever it’s kept in the idle condition, it is due to these following causes:

1. Restrictions in the carburetor:

A clogged carburetor can be one of the reasons when an engine is experiencing problems while idling. A carburetor’s job is to supply the engine with an air-fuel mixture in the right quantity. Due to various reasons such as low-quality fuel, low maintenance, dust build-up can cause restrictions in a carburetor’s jets. These blockages severely affect the quantity of the air-fuel mixture reaching the engine and, in turn, causes the engine to produce sputtering noises or even shut down in some cases.

– Solution:

• Cleaning the carburetor:

To service the carburetor, you should follow the steps below:

  • Unscrew the front cover: Unscrew the front cover and air filter door to view your machine’s carburetor.
  • Disengage the fuel lines: Afterward, you need to disengage the fuel lines leading to your carburetor. Be careful while removing the clamps so that no fuel leakage occurs. Also, there might be two screws that connect the carburetor to a linkage. They also need to be removed.
  • Remove the carburetor: Now that the carburetor has come off, carefully remove its screws and jets. It is advised that you make a video during disassembly or take some pictures to ensure that you don’t lose track of the parts removed. This will help you in reassembly.
  • Check the jets: Next up, you need to check the jets and screws for restrictions within due to dust and debris. For the cleaning of these holes, a carburetor cleaner liquid can be used. If available, you can also use compressed air for unclogging.
  • Assemble: Now, you should assemble the parts and put the whole assembly back in its fixed place.

2. Faulty Unloader valve:

A defective unloader valve can also cause engine problems while idling. The function of an unloader valve is to regulate the water pressure within the pump. When no water is being sprayed from the nozzle and the engine is running, water pressure builds up in the pump. The unloader valve diverts this high-pressure flow towards a low-pressure channel to reduce the backpressure on the pump. When the trigger is released, the valve allows the water stream to come out of the nozzle.  

If the unloader valve is defective, then very high pressure will build up in the pump during the no-spray condition, which will make it difficult for the engine to rotate the pump. Resultantly, the engine will undergo difficulty in operation, and it might eventually shut down during idling.

– Solution:

• Replacing the unloader valve:

To inspect the unloader valve, it first needs to be removed from the pump assembly. The pump can be made visible by unscrewing and removing the exterior of the washer. Once that’s done, you might see an unloader valve comprising of a spring-loaded plunger. You should inspect the valve for possible faults, and if they appear, the valve needs to be replaced with a new one.

Additional Causes:

1. Bad Fuel Quality:

For gasoline pressure washers, the fuel should not be left in the tank for more than 30 days as it can attract dirt and cause debris to assemble. This can further lead to the clogging of carburetor jets.

– Solution:

• Re-addition of fresh fuel:

If the fuel has been left in the tank for more than 30 days, it should be drained out. It would be best to clean both the tank and the carburetor (as explained above) and add fresh fuel back into the tank.

2. Dirty Air filter:

As a fuel filter, an air filter is a sponge-like filter situated in your pressure washer to filter dust particles in the air. If the engine does not idle, one reason might be that it does not receive an adequate supply of clean air. This is usually when the air filter is dirty with dust particles and needs to be cleaned.

– Solution:

• Cleaning the air filter:
  • Open the filter casing: The air filter casing is located right next to your fuel tank. Open the lid of the casing and remove the air filter. Remove any debris situated inside your casing.
  • Wash the filter: The filter might be dirty with oil and debris. A soap water mixture can be used to clean off the dirt.
  • Check for soap residual: Ensure that the filter does not have any soap residuals after cleaning.
  • Apply engine oil: Afterward, you should apply the engine oil (the regular that you use) onto the filter and press it gently so that oil reaches all the pores. This is usually done because the oil attracts all the dirt particles in the air and prevents it from reaching the engine.
  • If damaged, replace: If the filter seems damaged, buying a new one might be a good idea.

Related Questions:

1. How long can you continuously run a pressure washer idle?

It is recommended that pressure washers should not be kept going for more than three to five minutes. The idle running time can be different for different models. The key reason why a pressure washer is not allowed to run idle is that it overheats the engine. This overheating must be prevented at all costs as it can adversely affect the system components’ life. It is also better to stop leaving the engine idle and power it off if you need to quit while cleaning.


 2. Can you let a pressure washer running idle?

You should avoid keeping your washer working idle. When you pull the rope, the engine starts, and the pump begins delivering water through the hose at high speed. If the system is left idle, i.e., no spraying of water, this water will start to flow under pressure inside the pump. Eventually, the circulated water gets hotter and hotter. Most pumps have a discharge valve, i.e., when the temperature exceeds a certain degree, the hot water is released, and the colder water is drawn into the pump. Despite that, this continuous high temperature can damage the pump’s seals and O-rings, which may lead to oil leakage from the pump. Eventually, they might wear out and need to be replaced.

3. Why does my pressure washer keep stopping?

If a pressure washer does not start, the most probable cause is the engine’s absence of combustion, which does not provide a successful power stroke. This problem may be due to several reasons that are listed below.

  • Clogged carburetor: A clogged carburetor in which blockages prevents the air-fuel mixture to be sucked in an adequate amount
  • Blocked air filter: Dirt and blocked air filter that does not supply a clean air-fuel mixture to the engine
  • Blackened fire arrestor: Blackened fire arrestor due to soot screen that inhibits spark
  • Fuel tank vacuum: Vacuum formed in the fuel tank
  • Clogged fuel filter

4. Why does my pressure washer die when the trigger is released?

When a pressure washer is left to idle stalls instead of running, then the most common cause of the problem is a faulty unloader valve. When the trigger is not released, and the engine is running, the unloader valve directs the water flow back to the pump inlet to reduce the pump’s backpressure. When this valve is not moving freely, then the pump’s high pressure can stall the engine and thus shuts down.

– Solution:

• Fixing the unloader valve:

Remove the unloader valve from your pump outlet. Check if the piston is not jammed and is moving freely. If it is jammed, use a screwdriver to remove both the piston and the spring and clean them with alcohol. Afterward, fix them back into the pump assembly.

Final Remarks:

All in all, if a pressure washer engine does not run idle, then it points towards the fact that the load on the engine exceeds its power generated. This is probably when the unloader valve does not release the pump’s high-pressure flow or when the carburetor is clogged with dirt that inhibits a successful power stroke of the engine. In both cases, the root cause is a lack of proper engine maintenance. Timely maintenance of the machine parts twice or thrice a year apart from using fresh fuel will surely maximize your pressure washer’s life.