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Two-Stroke Engine Has No Spark: Why and How to Fix It

Two-Stroke Engine Has No Spark: Why and How to Fix It

Two-stroke engines are easy to start, so if yours does not spark or start when you kick or pull it a few times, it means that something isn’t right. Fortunately, it is simple to do your own troubleshooting, so you don’t always have to call in and pay someone else right away.

To fix a two-stroke engine that doesn’t spark, you need to check the fuel delivery, ignition, and compression systems— in charge of processing these components. Finding which system is the culprit allows you to fix the problem. 

You will, however, need to know how to inspect each of these systems. And what signs to look for if there is an issue. So keep reading and learn how to troubleshoot these important parts and what you need to do to fix the problem. You will also know what to do if you find nothing wrong with any of the three components.

Check Each System that Makes Up a Two-Stroke Engine

In the YouTube video tutorial below, eReplacementParts explains that the easiest way to diagnose the problem with your two-stroke engine is to think of it in terms of its systems:

How to Diagnose Two-Cycle/Two-Stroke Engines

All two-stroke engines consist of:

  • Fuel Delivery System. The fuel delivery system is in charge of delivering fuel to the cylinder. It is made up of the fuel or gas tank, the fuel lines that connect the tank to the carburetor, and the carburetor, which mixes the fuel with air and delivers it into the cylinder. 
  • Ignition System. The ignition system creates the spark for the ignition. It is made up of the ignition coil and the spark plug.
  • Compression System. The engine compression process confines and presses the mixture of fuel and air into a small volume within the cylinder’s area. This system is made up of the cylinder and the piston.

You can start checking the parts of each system that are most likely to fail. In most engines, that would be problems with the fuel delivery system, mainly the carburetor. It could also be the ignition system, which is mainly the spark plug. 

Test the Fuel Delivery System

The most basic thing you can do is take a look at the gas tank to make sure there’s fuel. Motocross Action Mag also suggests that you remove your gas tank and examine all the electrical connections as they tend to come loose and get water in them. 

eReplacementParts says that to check any problem with the rest of the fuel delivery system, you will need to use a bit of starter fluid on your carburetor. Remove the air filter first and make sure it is not clogged. This would rule out any problem with the airflow. Remember that a dirty air filter can impede airflow and disrupt the correct air-fuel ratio needed to start your engine.

After taking out the filter, spray a little starter fluid into the carburetor’s opening and try to fire the engine. 

If the engine fired for a short while but died almost immediately, it means that the starter fluid went through the carburetor, burned in the cylinder, and stopped when it ran out of fluid. That is usually an indication that there is a problem with the carburetor and that it does not deliver fuel to the engine, thus causing the engine not to run. 

A problem with the carburetor means that it either needs cleaning or it needs to be rebuilt. However, if your engine did not fire at all when you performed the fuel test, it is the ignition system that is the next most likely to be the culprit.

Test the Ignition System

Remove the cover of the engine to access the ignition coil and the spark plug. 

Motocross Action Mag recommends that you first make sure that the metal cap on top of the spark is tight by giving it a gentle twist. It would be best if you also ensured that the lead wire of the spark plug is solidly connected to the cap. 

You can also pull the lead wire out of the spark plug cap and check its end. If the core wire looks burned or is not visible, that could be the problem. Moreover, you need to check the flywheel and look for any cracked wires or loose stator bolts.

eReplacementParts, meanwhile, recommends looking into the spark plug and says that the easiest way to check it is just to replace it with a new one since spark plugs are cheap. However, there is an alternative, and that is to use a piece of testing equipment called spark tester, which you probably don’t have.  

Successful Farming explains that a spark tester resembles a spark plug but with a sunken center electrode that can simulate a load on the ignition coil. 

Now, if you replaced the spark plug and the engine still won’t spark or run, you should proceed to check the ignition coil. To do this, you would also need the spark tester. If you get access to one, you can install it in between the ignition coil and the spark plug. Attach one end to the boot of the coil and the other end to the plug. Pull the starter rope or kick it off and see if you get any spark. 

If you don’t see any spark in the window of your tester, it means that the coil needs replacement. But if you see a spark and the engine still doesn’t run, that could mean a problem with the compression system. 

Here’s a video on how to test the coil:

How to Test a Lawnmower Coil

Test the Compression System

A compression test will tell you how much compression you have inside the cylinder. To do this, you will need a compression gauge. Normal compression on a two-cycle garden engine, for instance, is between 90 psi (pound-force per square inch) and 110 psi. Anything beyond 120 psi is already too high. 

Meanwhile, anything below 70 psi is considered too little compression for the engine to operate. Make sure your gauge is at zero.

Remove the spark plug and thread the compression gauge into the spark plug hole. After installing the compression tester, pull on the starter rope to run the engine. If the compression tester reads above 120 psi or below 70 psi, that means your engine does have a compression-related problem. 

At the very least, you just might need to replace the piston rings. But the issue could be more serious, like a damaged piston or cylinder.

Fix the Carburetor or Fuel Lines

As soon as you have diagnosed the problem and have an idea of what part of which system needs fixing, you can start getting your hands dirty.

Problems in the electrical connections in the gas tank can be fixed by spraying them with contact cleaner, plugging them solidly together, and wrapping them with electrical tape so that they stay put.

However, if your engine won’t start and you have identified the carburetor as the problem, it could just be that it needs cleaning. Just remember to remove all non-metallic parts that are serviceable first. 

Here’s a video tutorial on how to clean the carburetor by eReplacementParts:

How to Clean a Two-Cycle/Two-Stroke Engine Carburetor

If you have cleaned the carburetor and put the removed parts back again, but the engine still won’t start, you can try adjusting the control cable or linkage to assure full choke and carburetor control.

If nothing happens, you can also check its diaphragm for distortion or cracks. You can also try adjusting the idle mixture screw or the main mixture adjustment screw.

You can also refer to this video on how to fix a garden carburetor:

How to Fix a Lawn Mower Carburetor

Meanwhile, this is how you rebuild a carburetor: 

How to Rebuild a Two Cycle/Two Stroke Engine Carburetor

If it’s your fuel lines that need to be replaced, here’s how:

How to Replace Fuel Lines on Two Cycle/Two Stroke Engines

Fix Ignition-Related Issues

Motocross Action Mag suggests that if the ignition shows any signs of dirt or moisture, you can start by cleaning it with contact cleaner then let it air dry. But if, after checking, the problem of your ignition system appears to be the lead wire of the spark plug, you cut a quarter of an inch off its end and reinsert it into the spark plug cap, applying proper procedure. 

You can refer to this video tutorial on how to trim the wire of your spark plug:

Trimming Spark Plug Wires from the coils for a 2 stroke Arctic Cat ignition

If it’s not the lead wire, you can also disconnect the kill button lead wire from the wiring harness. Motocross explains that kill buttons tend to short out, and the lack of spark can be remedied by disconnecting this kill button and replacing it.

You can learn how to replace the ignition coil from this video:

How to Replace Coil in 2 Stroke Pocket Bike Engine - Instructions PS50 Nitro Motors

Fix the Compression System

When you have determined that your piston is the problem and needs replacement, you can refer to this video tutorial to learn how to install a new one:

Trimmer Repair - Replacing the Piston & Rod Assembly (Ryobi Part # 753-04367)

If it’s the cylinder that’s the issue, here’s how you can replace it:

How to replace 2 stroke cylinder and piston (moped 50cc)

For newbies, however, doing piston and cylinder replacements can be tricky, so you might need to call in a professional mechanic to help you do the job.

Final Words

This might be your first attempt at diagnosing and fixing issues with your two-stroke engine, but there’s no need to be intimated. Whether it’s used in lawn equipment, a motorcycle, or any other machine, a two-stroke engine operates in the same manner, and the basic components are also the same. 

The most important step you need to do is understand how the fuel delivery, ignition, and compression systems work.

Once you understand how the systems function, it will be easy to learn how to troubleshoot and check them for any problem, solving the issue is more difficult, though. Because fixing problematic parts of the engine involves costs, one cannot afford a trial-and-error approach. 

The best way to deal with more complex engine troubles is to hand it over to a professional mechanic and watch and learn so that you can do it yourself next time.

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