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Dirt Bike Won’t Start Has Fuel & Spark: How To Fix It

You want to ride but your dirt bike won’t start but it has fuel and spark. Those are just 2 parts to the equation, and just because you’re getting fuel and spark doesn’t mean it’s the right amount.

In this article, I’m going to show you the practical steps I take to get a dirt bike running when it won’t start and how to start diagnosing the problem.

2 stroke has fuel and spark but won’t start

Have you confirmed that it’s actually getting fuel to and through the engine? From the gas tank, through the fuel line, to the carb float bowl, and into the engine, it doesn’t take much to clog a passage.

It’s easy to forgot to add gas to your dirt bike tank, especially if you don’t ride very often. Even if there is some gas left in the tank, it may not be high enough to get down through the petcock filter and to the carburetor, but there’s a simple trick you can do to see if that’s your problem.

Pro tip: You can either turn the gas petcock valve to “reserve” if it has that option, or you can lean your dirt bike way over almost onto its left side to get the gas onto the side of the tank that has the petcock. Both of these options will get more gas to your carb and possibly give you enough to get it started,

May 13 Dirt Bike of the Month KTM 300EXC Dirt Bike Won't Start Has Fuel & Spark: How To Fix It
A shiny bike is no good if you can’t start

Bike won’t start even with starting fluid

To confirm that it’s getting fuel, you can put a few drops of gas or starting fluid into the engine through the spark plug hole. On a 2 stroke, removing the spark plug is as easy as unscrewing the plug on most models.

For some 4 stroke dirt bikes you may have to remove the gas tank to access the spark plug hole. Otherwise, you can try squirting some starter fluid into the carb if it’s easier to pop it off of the intake boot.

If it still won’t start or make any kind of combustion noise, then you can confirm that it’s getting fuel but still not starting.
This means that it’s mostly likely not getting: spark, the right amount of air, enough engine compression.

Spark

If you have fuel, air, and compression but no spark or not enough spark then your dirt bike engine can’t ignite the mixture and it won’t start. “No spark” can be caused by a fouled plug, a loose plug cap, a bad wire, a faulty ECU, or a bad stator.
But first, let’s check to see if that’s the case, because no spark is not as common as the other problems.

By taking the spark plug out but setting it on the engine with the plug cap installed you can test for spark. Slowly kick or turn the engine over (in the dark makes it easier to see) and you will see a small blue spark jump across the electrode/tip of the spark plug.

If there is no spark, even in a dark room, the next step is to try replacing the spark plug. Perhaps the plug is fouled and just not creating enough or any spark to ignite the mixture.

A fouled plug can cause your dirt bike not to start
A fouled plug not getting enough spark to ignite the air-fuel mixture

Once you confirm that there your dirt bike is getting fuel and spark, it’s time to move onto the next step. But if it’s not getting spark, then you need to diagnose this electrical problem until you find the problem source and fix it.

Air

So, you’ve confirmed that it’s getting fuel and spark but your dirt bike still won’t start. The next step is to make sure it’s getting enough, but not too much air. It’s more than likely not getting enough air to and through the engine.

A dirt bike that has fuel and spark but won’t start might be caused by:

  • A rag in the airbox
  • An air leak
  • Blown head gasket
  • A plugged/clogged exhaust
  • Dirty air filter
  • Low compression
Dirty Air Filter causes spark plug to foul
Dirty air filters can cause more problems than you think

While these aren’t the only reasons why your bike isn’t starting, these are the things that I would look into first.

Whether it’s a pit bike bike or full-sized dirt bike, 2 stroke or 4 stroke, they all operate on the same fundamentals.

Engine compression

When you have the right amount of fuel, air and spark, it’s time to check the engine compression. When the compression gets too low, it can’t compress and combust all of the air and fuel – this causes a rich jetting mixture.

Low engine compression can also cause: rich jetting, spark plug fouling, and low power output.
This usually happens when the engine gets worn out or the head gasket fails from getting too hot.

To start and run properly, your dirt bike needs:

  • A clean and properly oiled air filter
  • A tightly sealed airbox/intake boot/carburetor
  • Jetting tuned for your specific bike, mods and climate
  • An engine with proper compression
  • The exhaust to be in good shape (relatively dent-free with proper seal and packing)

Did you change anything?

You also need to ask yourself if anything has changed since the last time you rode. Did this problem just start happening today? Did you do anything to your dirt bike, such as:

  • Remove the seat
  • Replace the air filter
  • Remove the gas tank
  • Change the exhaust

Any number of adjustments could’ve caused a change. Maybe you removed the tank and when re-installing it, an electrical connection got disconnected. Or you had a crash the last time you rode that broke the kill-switch.

Why does my dirt bike only start with starting fluid?

If you have to put starting fluid or a splash of gas into the cylinder to get it started, then the fueling system isn’t working properly. It’s not getting fuel to the engine, so you have to work your way down. 

If your dirt bike only starts with starting fluid, then check these:

  1. Clogged gas tank vent line (blow through it)
  2. Clogged petcock/filter in gas tank
  3. Clogged fuel line or inline fuel filter
  4. Dirty/clogged carburetor
  5. Low float level in carb
  6. Jetting is too lean

Dirt bike won’t start after sitting

Has your dirt bike been sitting for a few weeks, months, or even years? Pump gas these days is notorious for going bad very quickly. This means that if your dirt bike or pit bike ran before it sat, then the gas is bad and you probably need to drain and/or clean the carb and gas tank. 

Seals might be bad as well, but I wouldn’t replace anything until you know that it’s leaking. A proper carb cleaning requires you to take the carb off or your bike, but it’s not as hard as it may sound, especially if you have a 2 stroke dirt bike.

You can try using carb cleaner while the carb is still on the bike, but this often doesn’t work. A carburetor has many tiny passages and jet circuits, and spraying a cleaner from the outside won’t get into all of these passages.

All it takes is one little piece of dirt or old gas debris to cause starting problems, and the way I clean carbs is the best way to fix dirty carbs when just using carb cleaner and compressed air won’t.

Free dirt bike won’t start checklist

Still can’t get your dirt bike started or just want a quick-reference list for when your bike won’t start again? Click here to download my free checklist that you can follow step-by-step in minutes.