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2 Cycle Engine Starts but Won’t Stay Running? Let’s Fix It!


2 cycle engines are very common, but they sometimes have issues. How do you fix a 2 cycle engine that starts but won’t continue to run?

A 2 cycle engine may start but not stay running if the carburetor is malfunctioning, if the gas is old and dirty, if the fuel line is clogged, or if the spark plugs are dirty or broken. To fix each part, remove and replace or clean them. Then the 2 cycle engine should keep running.

Now that you know some of the reasons why a 2 cycle engine starts but may run into trouble later, you may be wondering exactly how to fix each problem. We’ll cover that below!

Carburetor

The carburetor is an important part of a 2 cycle engine. If it becomes broken, dirty, or loose then the engine may start but will soon stop running. If your engine is experiencing an issue like this, look at the carburetor and see if it is broken, loose, or needs to be cleaned.

Your problem may have a simple solution if you see that the carburetor is filthy. This piece of machinery can’t run properly if it is dirty. The problem can be fixed as long as the carburetor is undamaged. If it is broken though, it will inevitably need to be replaced. The exact process and carburetor will vary depending on the specific 2 cycle engine you are working on.

How to Fix It

If the carburetor is dirty, take it apart and use a carburetor cleaner and a rag to remove the buildup. Once the carburetor is completely clean, then you can reassemble it and attach it to the engine.

If the carburetor is just loose, simply tighten all the screws and bolts on every part and make sure it remains firm when it’s bumped or shaken. Once you’ve reassembled the carburetor, it doesn’t hurt to make sure that all of the bolts and screws are tightly screwed into the rest of the engine. If one part came loose, others could have as well.

If the carburetor needs to be cleaned even more, clean the float bowl as well.

Gasoline

If the gasoline in your 2 cycle engine is old or has any debris in it, then the engine may start but then stop running shortly afterward. The engine may also stop running if the vent on the gas cap is clogged. When the gas cap vent is clogged, gas can’t run through the engine because a vacuum forms and prevents the gas from flowing through the system.

How to Fix It

If the gasoline in your 2 cycle engine is old, remove and drain the gas tank into a bucket or large container and properly dispose of the old gas at a later time. After the old gas is drained, put the gas tank back and pour fresh new gas into the tank. This should allow your 2 cycle engine to continue running after it has started.

If you think that the gas tank has debris in it, you should also drain the gas tank. Before you drain the gas tank, if possible, take it off of the engine. After you have drained the dirty gas into a container to properly dispose of later, rinse the gas tank and the fuel pump with water.

If possible, use a small brush to clean off any leftover dirt and debris. Set aside the gas tank to dry completely. After the gas tank is completely dry, put it back onto the engine and fill it with new gasoline.

If the vent on the gas tank cap is dirty or seems to be clogged, gently clean it with soap and water. After you have cleaned it thoroughly, set it aside to dry. When the gas cap is fully dry, put it back onto the gas tank.

All of these fixes are relatively simple, but they can help out a lot. You can save yourself from a trip to the mechanic or hardware store just by doing some simple cleaning and maintenance at home.

For more detailed information, see Cleaning Gas Tank of Two-Stroke Engine.

Fuel Line

If your 2 cycle engine is starting but then stops, check the fuel line. If the fuel line is cracked, deteriorated, or clogged then the fuel line is probably the cause of your troubles.

How to Fix It

If the fuel line is deteriorated or cracked then it will definitely need to be replaced. You can find a replacement fuel line at most local hardware stores, but make sure you get the correct one. Bring the old fuel line with you when you go to purchase the new one. This will help you match the size and model of the original.

If the fuel line is clogged, use a thin long cleaning brush and try to clear the blockage. If you can’t get the clog out with this method, it will need to be replaced as well.

Old Oil

If your 2 cycle engine has been having problems and you know that the oil inside it has not been changed in a long time, the oil may be causing the trouble. Old or dirty oil can cause major problems for any engine, so make sure you investigate this possibility. Yes, two-stroke oil does go bad (source).

How to Fix It

If you think the oil may be the problem, change it. In order to change the oil, find the oil reservoir and the plug that holds the oil in. Remove the plug and drain the old oil into a bucket to be disposed of later.

The darker the oil is, the older and dirtier it is. After the old oil is completely drained, put the plug back in and refill the oil. You can find oil for a 2 cycle engine at any local hardware store.

Spark Plug

Another potential culprit behind your engine troubles is your spark plugs. If they are dirty or broken, your engine will have a hard time running continuously. If the spark plugs are defective, the engine just can’t keep running.

If you suspect that the spark plugs are causing the engine to stop running, go into the engine and remove the spark plugs. If they are dirty or seem to be broken, then they are likely the cause of your engine stalls. Luckily, these items are easy to replace.

a spark plug with debris or corrosion may inhibit the spark-combusion-compression process needed for a two-stroke engine to run.

How to Fix It

If the spark plugs are dirty, wipe them down with a gentle cleanser and a rag until they are clean, or at least until you think that they are clean enough to function properly.

If they cannot be cleaned enough to work properly, throw them away and purchase new ones at a local hardware store. Spark plugs cost an average of $5 each, so they are relatively cheap.

When you have the new spark plugs, screw them in tightly and your 2 cycle engine should run properly again.

Air Filter

Another piece of equipment that could cause engine trouble is your air filter. If the air filter is dirty or clogged, the engine can’t run properly and will die after it has started. Air has to flow through the system to properly remove the gases that are produced within. Luckily, the air filter is very easy to replace.

How to Fix It

If the air filter in your 2 cycle engine is dirty or clogged, simply replace it. Remove it from the engine and replace it with a new one. Make sure it is installed properly and securely and then you should be good to go. Throw away the old air filter. You can find replacement air filters at any local hardware store.

Broken Gaskets

If your 2 cycle engine starts but then stops running, the gaskets may be broken or leaking. Gaskets help keep the chambers in the engine airtight, and if they are broken then air can get into the engine when it is not supposed to. This can cause the engine to stop running, even if everything else is working perfectly fine.

How to Fix It

If the gaskets in your 2 cycle engine are broken, then they will need to be replaced. You can purchase new ones at any local hardware store. In order to replace the gaskets, remove the old or broken ones with a wrench. After you have completely removed the old gaskets, put in the new ones and tighten them with the wrench. Make sure that they are all tightly screwed in.

Exhaust Ports

When you’ve having engine troubles, then the exhaust ports of your machine may need to be cleaned. If the exhaust ports are dirty or clogged, then the exhaust can’t escape and the engine will stop running after a while.

Exhaust ports exist to channel troublesome gas and debris away from the engine, so you will definitely run into issues if it develops a blockage. Luckily it is very easy to clean the exhaust ports and you won’t need to go super far out of your way to fix this problem as long as you are dealing with an exhaust that is cracked or leaking.

How to Fix It

In order to clean the exhaust ports, remove the muffler, as the exhaust ports will be found underneath it. Use a clean and dry bristle brush to gently knock away all dirt and debris that is blocking the flow of the exhaust port.

After the exhaust port is clean enough to let gas escape, manually turn the engine in order to get any excess carbon granules out of the engine. Then replace the muffler and try to run the engine for a while. If the muffler was your issue, cleaning it out should have solved the problem. (Source)

Old or Flooded Engine

If your 2 cycle engine starts and then stops running, then the engine may be flooded. In order to tell whether or not the engine is flooded, remove the spark plugs. If the spark plugs are wet, then the engine has flooded.

If your 2 cycle engine is flooded it may be probably dead and the gaskets need to be replaced. However, if your engine is more than 10 years old you may not be able to find a gasket that will fit your engine, which will make it nearly impossible for you to make your 2 cycle engine run properly again.

How to Fix It

If your 2 cycle engine is flooded, you will need to allow the cylinder to completely dry before you try to use the engine again. In order to make it dry faster, take out the small pieces that you can remove and let them dry for at least a few days. If you continue to try to use the engine while it is flooded, you will ruin it even further until it is beyond repair.

If you can’t locate gaskets that will work with your 2 cycle engine then you may need to buy a sheet of gasket material and make new ones that will fit in your engine. If you need to make new gaskets, use the old gaskets that you removed from your 2 cycle engine as a pattern, and you will have new gaskets that will fit your engine. Gaskets are fairly simple to make as long as you have the right materials and guide.

For more information read How to Diagnose and Fix Two-Stroke Flooding Problems.

What if Nothing I Have Done Worked?

If none of the repairs have allowed your 2 cycle engine to run properly again, the engine may be misfiring. Make sure that all parts of your engine are properly tightened, cleaned, and greased up so they can function properly.

If you have checked and replaced everything on this list and your 2 cycle engine still is starting but stops after a while, then take it to a licensed mechanic and have them take a look at it. They will likely be able to diagnose the problem and be able to fix it. They will also tell you if your engine is too old or worn out to fix, and if any repairs can be made (or if they are even worth it). Make sure that the mechanic you take the engine to knows how to deal with a 2 cycle engine.

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Teddy Henderson

Teddy is always fiddling with small engines, picking up thrown-out string trimmers or tearing apart dirt bikes. He shares what he learns along the way. Hopefully, you'll have less headaches than he has had by learning from his mistakes.

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