We find 2-stroke engines in all sorts of gadgets— chainsaws, motorbikes, weed-eaters, go-karts, even ultralight airplanes. With so many of them in our lives on a daily basis, we can expect that a time will come when one of those 2-stroke engines you depend on won’t start.
Here are 7 problems that might cause your 2 stroke engine not to start:
- No fuel
- Too much fuel
- No spark
- Choke lever in the wrong position
- No air
- Air leaks in the engine
- Carburetor issues
I’ll look at how to address each of these issues and get your 2-stroke engine running again. Read on to diagnose and fix your 2-stroke engine’s failure to start.
1. No Fuel
Okay, so most of us (whether we’ve admitted it to anyone or not) have, at some point, struggled with an engine only to realize, embarrassingly late, that there was no gas in the tank. Don’t fret. It happens. But then you fill it up, set the choke, pull on the engine, and you’re up and running.
That’s the easiest fix. However, you might encounter a problem where the engine isn’t getting gas even though your fuel tank is full. Check the primer bulb if your 2 stroke engine isn’t starting, but you know there’s gas in the tank. If there’s nothing in there, you’ve got a fuel line problem. You can check out this video explaining how the primer bulb works:
Check your fuel filter, which may be clogged and in need of replacement. If the filter has been in use long enough, all the things it’s been filtering out of the fuel can build up on the filter so that no fuel can get past that spot.
If the filter needs replacing, it’s an easy fix, though you’ll need to get the right filter for your engine. A quick search on Amazon.com brings up any number of filters, and you can quickly narrow down the field of choices to the right fuel filter for your 2 stroke engine.
If the issue lies with your fuel lines— they’re clogged or maybe have a leak— they are relatively easy to replace, as well (source).
But before you start disconnecting things, check your fuel tank. Maybe make sure no one is around to see you do it, but make extra sure the issue causing your 2 stroke engine pull start problems isn’t that it’s out of gas. So embarrassing.
Also see What To Do if a 2 Stroke Isn’t Getting Enough Fuel.
2. Too Much Fuel
If you get too much fuel in the combustion chamber, your engine won’t be able to start. Remember that a 2 stroke engine burns a fuel mixture of gas and air, so if too much gas gets into the chamber, the spark plug won’t be able to make enough of a spark to ignite the fuel mixture.
The most significant indicator of flooding isn’t that the engine won’t start. After all, your engine could have any number of issues, as there’s a lot to go wrong in a 2 stroke engine.
The easiest way to diagnose it is with your nose. If your engine won’t start and you notice a gasoline smell, you’re almost certainly dealing with a flooded engine.
Causes of Flooding
Most 2 stroke engines have a primer bulb that, before you try to start it cold, pushes fuel into the combustion chamber so there’s gas ready to be ignited for that first engine start of the day. However, you’ll flood the engine if you pump too much fuel in there.
Flooding can also happen if the choke is closed while you try to start a cold engine, as that cold engine needs a little more air in the fuel mixture than a warm engine does. When the choke is open, the valve allows extra air into the chamber. Without that excess air, your engine can quickly build up too much fuel and then refuse to start.
If your air filter is dirty, that can also cut down on the amount of air in the mixture too, and a blocked carburetor can also cause flooding.
Fixing the Flooded Engine
If the issue is that you overprimed the engine or that you forgot to open the choke, the easiest fix is to wait a bit. Given time, the extra fuel will evaporate from the combustion chamber. Once the extra fuel leaves the chamber, you won’t have a flooded engine anymore, and all will be right with the world.
If you don’t have time to wait, another solution is to pull the spark plug and replace it with one like this JRL Spark Plug (available on Amazon.com). I like this particular product because it’s affordable and gets the job done. The problem likely isn’t that the plug needs replacing, but that it’s gotten wet from the excess fuel.
Pulling the plug out and drying the business end of it will almost certainly allow the engine to fire up despite the extra gas, but it’s not quite that simple, as you’ll need to do a couple of things:
- Remove the plug (if you’re using a chainsaw, the scrench included with your saw has a spark plug wrench on one end of it).
- Close the choke and pull the engine a few times (without the spark plug, you can’t possibly start the engine, but you’re pulling on it to help clear the combustion chamber).
- Dry the plug and reinstall it in the engine.
- Start ‘er up.
If the issue lies with your carburetor, you may find that disassembling and cleaning it is above your pay grade. If you’re comfortable with the task, keep in mind that it’s a long and labor-intensive process, and if you don’t put everything back together just right, you’ll have problems. If you’ve ruled out all the other causes of flooding, you might want to take the engine in for service (source).
3. No Spark
I’ve touched on this a little already, but if the spark plug can’t fire, you can’t get the necessary combustion that makes a combustion engine, well, a combustion engine. While the flooding issue can easily make the spark plug too wet to function properly, your engine might not start because the spark plug isn’t working correctly for several other reasons.
| Symptom | What’s Happening | Cause | Possible Solution |
| Black carbon deposits. | Fuel isn’t burning completely, and the leftover materials build up on the plug. | The choke may be stuck somewhat open, there may be carburetor issues, or your spark plug wire may be faulty | Check that the choke valve and carburetor work properly; they may need service. Replacing the spark plug wire may be necessary. |
| Chipped insulator. | Pre-detonation is occurring in the engine. | Ignition timing issues, engine overheating, or a clogged combustion chamber. | Address the combustion chamber first, then check for possible causes of overheating, and finally, adjust the timing if necessary. |
| The electrode is broken or misshapen. | The plug doesn’t fit your 2 stroke engine. | You have the wrong size plug. | Check your owner’s manual for the correct part number and install the right size. |
| Oily black buildup on the electrode. | Oil has made its way into the combustion chamber. | Worn piston rings or other gaskets. | Check (and likely replace) the faulty gasket. |
| The plug is wet. | The engine is flooded. | See above. | Dry it off. |
| White or blistered tip | Melting has occurred. | The engine runs too hot. | You’ll need to replace the plug and remedy the running-too-hot issue. |
| A yellow glaze on the electrode | The buildup cuts down on the plug’s ability to conduct electricity. | The engine runs too hot. | Spray the plug with brake cleaner, let it soak, then wipe it off. |
Also see Two-Stroke Engine Has No Spark: Why and How to Fix It.
4. Choke Lever in the Wrong Position
You use the choke valve in a small engine to enrich the fuel mixture to a higher level the engine typically uses. When fuel enters the carburetor, it needs to evaporate to combust most efficiently. Still, when the engine is cold (like when you’re beginning your day of chainsaw operation), the fuel doesn’t evaporate properly.
So you need a way to let air into the carb. With more air, there’s less room for fuel. If the fuel isn’t evaporating properly, you can put more fuel in the chamber to get it to combust.
This is what the choke valve does— it chokes the engine, allowing less air to flow in, creating a higher level of fuel to be present. Combustion starts, the chamber warms, and the fuel can properly evaporate into a gas and ignite properly.
If your engine is cold and the choke valve is down (where it sits during the normal operation of the 2-stroke engine), it won’t start no matter how hard you pull on it (source).
5. No Air
Admittedly, this cause is pretty rare, but it does happen. Knowing what we already do about the necessity of air in the fuel-air mixture that makes a 2 stroke engine run, you know you have to get air into the engine along with the fuel.
Without enough air, you can experience a buildup of carbon in the engine and on the spark plug, or you can find yourself pulling on the starter rope until your shoulder hurts and never get the engine running.
You’ll need to check the air filter. If it’s too dirty, it may not allow enough air to pass through it to mix with the fuel. A no-air issue is rare because even the dirtiest filter still lets something through it. But you could have a foreign object in it or on it, which would completely impede airflow (source).
6. Air Leaks in the Engine
I’ve spent time already discussing the importance of the correct mixture of air and fuel, so if your engine has air leaks in it, it may not be receiving enough fuel to combust. A minor leak will not prevent your 2 stroke engine from starting, but it will undoubtedly contribute to the engine running inefficiently.
Since the hoses on most 2 stroke engines are mostly rubber, they’re not indestructible. Age, wear and tear, and even a significant blow to the engine (from dropping your chainsaw, for example) can cause minor tears in the rubber. With so many moving parts in a 2 stroke engine, lots can go wrong, and so many possibilities for wear exist in the whole process.
The following can also allow too much air into the engine:
- Loose fittings
- Old and brittle gaskets
- Bad seals
The best way to fix this is actually in preventative maintenance. Most of our dads or granddads said to us at some point in our lives, “If you take care of your things, your things will take care of you,” and that’s true when it comes to 2 stroke engines. Maintaining your two stroke engine is the best way to ensure it will start consistently when you need it.
7. Carburetor Issues
The carburetor is a complex and precise fixture on your 2 stroke engine, and sadly, the slightest misconfiguration can cause the engine not to start. The carburetor relies on the Venturi effect, which uses constriction of the tube the (in this case) fuel flows through to increase its velocity.
The bottom line with carburetor issues is that if you don’t have experience working on carburetors, you probably don’t want to mess with it on your own. If your engine won’t start, but you know it’s not any of the other issues on this list, the chances are that the carburetor is the problem.
Remember that the vibrations from the engine can slowly but surely loosen screws in the entire contraption, and when this happens in the carburetor, things can get out of whack pretty easily. Tightening any loose screws and then recalibrating the carb will probably fix the issue unless there’s something seriously amiss.
In either case, if you’re not comfortable doing this on your own, invest in a professional’s assistance, so you don’t have to invest in a brand new dirt bike engine or a new leaf blower or whatever you’re running.
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