Skip to Content

This is Why Your Shindaiwa String Trimmer Runs Rough: SOLVED!

You may call it a weed wacker, weed whip or weed eater. No matter what you call it, you will most likely run into a time where your string trimmer begins to run rough. This is a common problem that can affect all gas-powered string trimmers causing a lack of engine power and poor performance.

A Shindaiwa string trimmer runs rough when it isn’t able to get the air, fuel or spark required to run smoothly. This is due to a plugged air filter, bad spark plug, clogged fuel line, bad fuel vent, old fuel, bad fuel filter, dirty carburetor or plugged spark arrestor.

Before performing any repairs, remove the spark plug boot, wait for the engine to cool and for all moving parts to stop.

This post may include affiliate links. Purchases made through these links may provide a commission for us, at no extra cost to you. As an Amazon Associate we earn from qualifying purchases.

Follow all safety instructions provided in your equipment operator’s manual prior to diagnosing, repairing or operating. Consult a professional if you don’t have the skills, knowledge or are not in the condition to perform the repair safely.

8 Reasons Your Shindaiwa String Trimmer Runs Rough & Bogs Down

Old or Bad Fuel Causes a Shindaiwa String Trimmer to Run Rough

Many people think fuel is just fuel and it doesn’t matter what type you use. Well, they are wrong. It does matter when you want to minimize potential fuel issues and have a good performing string trimmer.

Using the wrong type of fuel in your Shindaiwa can cause significant problems including damaging the engine and having to replace your string trimmer. Shindaiwa string trimmers use a gas and oil mixture at a ratio of 50:1.

Always use a fresh unleaded gas with a minimum octane rating of 89 and a maximum ethanol content of 10%. Mix with a 2-cycle premium oil like ECHO Power Blend or ECHO Red Armor. Using straight gas will damage the engine.

Old gasoline and ethanol can cause your Shindaiwa to run rough due to these reasons:

  • Ethanol attracts moisture to the fuel system.
  • Moisture in the system causes corrosion.
  • Old fuel leaves behind a varnish and gummy deposits that restrict the fuel supply by clogging and preventing fuel components from functioning correctly.

Because gasoline breaks down as quickly as 30 days after purchase, it is important to purchase fresh gas and consume it within this time. If you are unable to use a tank of fuel this quickly, add a fuel additive like Sea Foam to stabilize it and reduce the negative effects of fuel so it last a little longer.

Some 2-cycle oils include a fuel stabilizer. Read the information on the bottle of oil to see how long the additive will keep the fuel stable. It can vary from 30 days to 2 years.

Read more about the right gasoline to use in “This is the Type of Gas and Oil Shindaiwa String Trimmers Use“.

Dirty Spark Plug Causes a Shindaiwa String Trimmer to Run Rough

A fouled spark plug on your Shindaiwa can cause it to misfire and run sluggish. A damaged spark plug, an incorrect spark plug gap and a loose spark plug wire can also result in running problems with your string trimmer.

Remove the spark plug using a socket wrench. Check its condition. Replace the spark plug if you find the tip is very dark in appearance, the porcelain is cracked or the electrode is burnt.

If the plug is in overall good condition and just a little dirty, you can clean it using a wire brush. Because the spark plug plays a major role in the running of the trimmer and is an inexpensive part, I always choose to replace it.

Check the spark plug gap using a feeler gauge to make sure it matches the manufacturer’s required specification. Install the new or cleaned spark plug. Make sure the spark plug wire is securely attached.

Plugged Fuel Filter Causes a Shindaiwa String Trimmer to Run Rough

A Shindaiwa has a fuel filter attached to the fuel line to keep any dirt or debris in the fuel from entering the fuel system. This filter can become plugged when it isn’t changed out regularly. A plugged filter will prevent a steady flow of fuel through the lines because fuel isn’t sufficiently able to pass through it.

A plugged Shindaiwa fuel filter must be replaced. Set the trimmer on a flat surface, wipe around the fuel cap and then remove it. Pull the fuel filter out of the tank.

Use a clean bent wire to hook the fuel line and “fish” the filter out of the tank. Once out of the tank, hold the fuel line and ring clip in one hand, securely grab the filter with the other hand and pull it out of the fuel line.

Do not lose the ring clip and keep it on the fuel line. Install a new fuel filter into the end of the fuel line. Make sure the ring clip is securely holding the fuel line to the male end of the fuel filter.

Clogged Fuel Lines Causes a Shindaiwa String Trimmer to Run Rough

Inspect the fuel lines and look for a clog or a kink that restricts the amount of fuel that is able to flow through the lines. Clogs can develop from dirty fuel or gummy deposits left behind by running old fuel.

Replace a line with a new fuel line when you find a clog, kink, puncture or leak in the line.

Plugged Fuel Tank Vent Causes a Shindaiwa String Trimmer to Run Rough

Your Shindaiwa trimmer will use a fuel vent that allows air to pass through it and into the tank. When the vent no longer works or gets plugged, the fuel tank will form a vacuum. This vacuum will prevent fuel from flowing out of the tank.

An engine that is no longer able to get enough fuel will run rough and possibly shut down. If you checked your fuel filter, fuel lines and carburetor and don’t find a restriction, you may have a bad fuel tank vent.

You can test for a plugged fuel vent by loosening or removing the fuel cap to allow air into the tank. Start the trimmer, and allow it to run. Be careful and keep your string trimmer level so you don’t spill any gas from the tank.

If your Shindaiwa trimmer runs strong and doesn’t bog down and run rough, tighten the fuel cap and see if you can replicate the issue to confirm the fuel tank vent is the problem. Replace the fuel tank vent if your trimmer starts to act up and run rough again after reinstalling the fuel cap.

Plugged Air Filter Causes a Shindaiwa String Trimmer to Run Rough

A Shindaiwa engine requires air to run. Without enough air, the string trimmer will run sluggish and rough. One of the items that can restrict airflow is a plugged air filter. The air filter can become plugged from dirt and debris when not regularly cleaned and changed.

If you find your air filter is plugged, I recommend replacing the filter and pre-cleaner. These small filters are not very expensive. It is an important component when it comes to protecting the engine. You may also choose to clean the filter if it is not damaged.

Clean a Shindaiwa string trimmer felt air filter:

  • Remove the air filter cover and remove the air filter.
  • Wipe any dirt or debris remaining in the air filter cover or housing.
  • Brush dirt off the air filter.
  • Install the clean filter.
  • Reattach the air filter cover.

Clean a Shindaiwa foam pre-cleaner filter (if your model uses one):

The pre-cleaner can be cleaned with water and a mild dish detergent solution. Rinse clear and squeeze to remove all water. Allow to dry before installing. DO NOT ADD OIL to the pre-filter.

Because there are so many different types of filters used which varies from model to model, refer to your operator’s manual for steps to clean the air filter for your string trimmer.

Dirty Carburetor Causes a Shindaiwa String Trimmer to Run Rough

The carburetor mixes the correct proportion of air and fuel needed for your Shindaiwa string trimmer to run. The passageways can become clogged and the small components can fail to function correctly. This can cause an insufficient amount of fuel mixed with air resulting in a rough running string trimmer.

You may be able to clean your carburetor to getting it working again. However, you may end up having to rebuild (if rebuild kits are available for your carburetor) or replace the carburetor if cleaning doesn’t help.

Damaged carburetors due to old fuel running through them is a common issue. One that can be minimized by using fresh fuel and properly caring for that fuel.

Plugged Spark Arrestor Causes a Shindaiwa String Trimmer to Run Rough

There is a small metal screen that keeps hot exhaust material from shooting out of the string trimmer and causing injury or starting a fire. This small screen will become plugged with a carbon buildup that will affect how the engine runs.

Disconnect the spark plug wire. Remove the engine cover and the engine exhaust cover. Carefully remove the spark arrestor screen. You can either clean it with a metal brush or a torch.

If you choose to use a torch, protect your hands and eyes. Hold the screen away from your body using pliers. Torch the screen to burn off soot buildup. Wait for the screen to cool and reinstall it. Reattach the engine exhaust cover and engine cover. Reattach the spark plug wire.

If the screen isn’t able to be sufficiently cleaned or you find it is damaged or has a hole in it, replace it with a new spark arrestor screen.

Service Your Shindaiwa String Trimmer to Keep It Running at Its Best

Keep your Shindaiwa string trimmer running at its best by performing an annual tune up. This includes replacing the maintenance items (air filter, fuel filter and spark plug); cleaning the trimmer; and replacing missing or damaged parts.