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13 Reasons Why Your Dirt Bike Won’t Start & How To Fix It

Wondering why your dirt bike won’t start, what it means, and how to get it running? Whether you just pulled the bike out of a barn after it’s been sitting for years, it just randomly quit running, or somewhere in between, you’re in the right place!

In this article, I’m going to share with you all of the most common reasons why your dirt bike won’t start (Free checklist), how to fix it so you can go riding, and some easy tips to prevent it from happening again!

These tips and tricks are based off of my 20+ years of experience owning, riding, and working on dozens of different dirt bikes, as well as street bikes.

Dirt Bike won't start on the trail
Having your dirt bike not start on the trail is the worst…

Why Won’t My Dirt Bike Start?

In order for your dirt bike to start it needs spark, a proper mixture of air and fuel, and enough compression from the engine. If your dirt bike is not getting just one of these, you can kick it over all day long and it still won’t start.

To save some possible time, we’ll take a quick look at each of these areas to see if you can spot something simple.

That way you won’t spend an hour trying to fix one thing when the problem could be something completely different.

If you prefer to watch a video over reading content, check out our video below to find out how to get your dirt bike started.

Oxygen – Your Dirt bike Needs Air

Air comes first, so pop the side cover and/or seat off and take a look at the air filter. Is there a complete air filter there?
Mice can easily get into the airbox during storage and make a nice “welcome nest” for you.

Dirty Air Filter causes spark plug to foul
Is your air filter or air box dirty?

It’s also easy to stuff a rag in there while working on the bike and forget to remove it when you put everything back together.

All I can say is, stranger things have happened, and it’s always safe to check first, especially since it only takes a minute.

A Clean Filter Is A Happy Filter

If the air filter is there, how dirty is it? If it’s caked with sand and mud, that alone could be causing your dirt bike to no run.

Clean or replace the filter and try starting it again.

My Dirt Bike Wont Run Diagnosing A No Start 13 Reasons Why Your Dirt Bike Won't Start & How To Fix It
This filter looks a little dirty…

Are You Leaking?

A less-common, yet possible cause, could be an air-leak in the system. Check the intake boot for cracks, as well as any bolts or gaskets in between the airbox, carburetor, and engine.

Over time, this rubber gets hard and will crack. It’s not always easy to see it, but if you wiggle the carb or spray some brake cleaner around it with the engine idling, the RPM will change.

You can also see in the picture below that the carb isn’t fully seated on the intake manifold. It should be fully pressed in or dirty and air can easily get into the engine and cause major starting and running problems.

TTR125 Mikuni VM24 Carb Swap Best Bang For Your Buck 2 13 Reasons Why Your Dirt Bike Won't Start & How To Fix It
Inspect the air box, carb, and intake manifold for leaks or loose clamps

2 Stroke Reeds Leaking Air

On a 2 stroke engine, the reed valve has pedals that wear out over time. They can last hundreds of hours if the bike isn’t ridden hard, but if the edges are chipped off, it could let unwanted air through and not allow the bike to start.

This takes longer to remove and inspect, but it’s just one of the many reasons why your dirt bike won’t start. Below shows the edge of a reed petal chipped – this needs to be replaced if you want your 2 stroke dirt bike to start and run properly!

A chipped reed petal from a 2 stroke dirt bike reed cage
A worn/chipped reed petal on a 2 stroke

Fuel – Not Enough or Too Much?

The engine requires air and fuel in order for combustion to occur, so the next step is make sure the engine is getting gas/premix. First place to check is the gas tank.

Is the tank clean with fresh gas? Gas or premix that has sat for a number of weeks will degrade and start to gum up.

If the gas smells like old paint, dump it out before doing anything and clean the tank out.

Dirt bike won't start because of dirty carb and jets
Dirty gas clogs up the carb jets and circuits

Fuel must go through the petcock to get to the carburetor. If the tank is empty, now is a good time to take a peek at the seal and filter screen on it.

Replace them if they are damaged, it leaks, have deteriorated or are missing with new parts/assembly. A the gas line that is cracked or plugged needs to be replaced as well.

Petcock deteriorated from bad old gas in dirt bike
What happens when you leave pump gas in the tank for years.

Are You Jetted The Right Way?

A dirt bike with poor jetting can not only prevent it from starting, but it won’t run well and will do more damage over time. Rich jetting will cause the engine to flood over easily.

Flooding the engine is when too much fuel gets into the cylinder/combustion chamber. Too much fuel and not enough air and you’ll just be kicking it over with no success.

How To Kick Start A Dirt Bike 13 Reasons Why Your Dirt Bike Won't Start & How To Fix It
Repeated kicks without starting can cause flooding

Continuous start attempts will also flood the engine with even more fuel, making your situation worse. If the engine is flooded, it’s best to wait for the fuel to evaporate.

You can try starting it again after sitting for at least a few minutes. If it backfires, then there’s still most likely too much fuel.

2 stroke has fuel and spark but won’t start

You’ve confirmed that the gas is getting to the carb, and the spark plug is properly igniting, but your 2 stroke dirt bike won’t start. The most common causes are a dirty carb or low compression.

Keep reading to learn how to properly fix a dirty carb. Low compression is the result of a worn top end.

Battery Just Clicks?

Electric start dirt bikes have a battery that powers the starter. If the battery has a low voltage or charge then it may not have enough power to start the bike.

It will either spin the engine over slowly or you will hearing a “clicking” noise from the battery. This means it needs to be charged or replaced.

If you don’t ride very often and your dirt bike doesn’t have a back-up kick starter, you should consider getting a battery tender (Amazon). They’re cheaper than a new battery and you can use it on any dirt bike or recreational vehicle in your garage.

A battery tender is better than a charger because it won’t overcharge the battery, which may ruin it or shorten its life. Lithium batteries require a Lithium specific battery tender.

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Won’t Start When Hot

A dirt bike that won’t start when hot is often a sign of the engine getting flooded. A rich jetting mixture is one of the main causes for a flooded engine.

The pilot jet is the most important jetting circuit when it comes to starting your bike. To learn more about how jetting works and to get your dirt bike running better go here.

Not Too Rich, Not Too Lean

On the other hand, if the jetting is too lean then the engine isn’t getting enough gas to start it. Try adjusting the air screw or fuel screw on the carb to allow more gas through the carb.

If that doesn’t work then the pilot jet may need to be swapped for a larger size.

Use Quality Gas

Next up is the carburetor, which is the root cause of many ‘no-start’ situations. Dirt bikes with smaller carbs, jets and passages can gum up in a matter of weeks because of old gas sitting in it.

Even if you can see through the pilot jet, there may be just enough crud stuck on it to not allow enough gas through to ignite the engine.

Using high quality gas will make your dirt bike run better and cause less problems in the long run.

Pre Mix 101 1 13 Reasons Why Your Dirt Bike Won't Start & How To Fix It
Use fresh gas and pre-mix if you want it to run well

Regular pump gas is full of so many additives these days that break down in short time. Once the gas breaks down it will cling to your carb and clog the jets and passages.

A good quality gas will have no ethanol in it, so look for that on the pump when filling your gas can. Non-oxygenated gas works very well in dirt bikes and other performance machines.

It will run the most consistently and last longer than regular pump gas before breaking down and going bad.

Cleaning The Carb

Carb cleaner and compressed air are your friends if the carburetor isn’t too filthy. You can sometimes just loosen up the carb clamps and rotate it to spray out the jets while still on the bike.

This can be done in a matter of minutes by removing the float bowl on the bottom of the carburetor.

Confirming Your Carb Needs A Thorough Cleaning…

If that doesn’t work, you may need to take the carburetor completely off and dis-assemble it for a more thorough cleaning. There’s a couple more quick ways to confirm that the carb may be dirty.

With starting fluid or a little bit of gas (half a spoonful is enough) down the spark plug hole try starting it again.

If it starts or runs for a second or two then you know it’s not getting gas from the dirty carb. You can also try and push start your dirt bike.

Video tutorial on how to push (bump) start a dirt bike

The Best Way To Clean A Carburetor

I have cleaned many dirt bike carbs over the years, and the best addition to my tool crib for this was an ultrasonic carb cleaner. For less than 100 bucks you can clean all the dirty carbs for years to come without having to pay a shop to do it.

All of the carburetor parts removed for cleaning a Keihin 2 stroke dirt bike carb
I remove all the main parts when cleaning a dirt bike carb

An ultrasonic cleaner penetrates all the old gas and dirt that gets stuck in the tiny passages that are sometimes impossible to clean with just carb cleaner spray (which I rarely ever use anyway).

It will pay for itself after cleaning just one or two carbs. If the carb is really dirty, then your dirt bike will start easier, idle better, and run stronger with better throttle response after a deep cleaning with the right solution. To buy your ultrasonic cleaner on Amazon click here or the image below.

I always use Simple Green Industrial cleaner & degreaser (Amazon) because it’s strong enough to clean old gas and it won’t hurt your carburetor.

q? encoding=UTF8&MarketPlace=US&ASIN=B01NCJ0N6O&ServiceVersion=20070822&ID=AsinImage&WS=1&Format= SL250 &tag=dirt bike wont start 20 13 Reasons Why Your Dirt Bike Won't Start & How To Fix It

If neither of those work, it may not be a fuel problem after all, but lets move on to one more quick check if cleaning the carburetor isn’t your solution.

Does your dirt bike have spark?

Your dirt bike may be getting air and fuel, but if there’s no spark, it won’t even want to start. A quick way how to check if a dirt bike has spark:

  1. Remove the spark plug from the engine.
  2. Put the cap back on the spark plug.
  3. Resting the spark plug on the engine .
  4. Slowly kick/turn the engine over.
  5. You may need to turn off the garage lights to see it.
  6. Look for a small, blueish spark of electricity on the end of the spark plug.

If you don’t see anything, be prepared to spend some time swapping out parts if you don’t want to replace everything in the electrical system.

Troubleshooting No Spark

If you know someone with the same bike, ask if you could temporarily swap some electrical parts off of theirs. It could be as simple as a faulty kill switch, or a bad ground in the system.

However, you may have to swap out the CDI box or even the stator to find the root problem.

XR600 Stator 13 Reasons Why Your Dirt Bike Won't Start & How To Fix It
Testing the stator may be necessary if the CDI box is still good

Once you find the part causing the problem, order a new one and give your generous friend back his/her parts, as well as taking them out to lunch if they lent you a hand in your project because they could have saved you a lot of money by not ordering the wrong parts.

Finally get your dirt bike started but now it won’t stay running? Click here to find out why!

My Dirt Bike Still Won’t Start!

If you still can’t figure out why your dirt bike won’t start, there’s a good chance that the engine needs some attention. Parts wear out after many hours on them, and a worn out engine can cause a dirt bike not to start or run well.

Low compression is common on motocross bikes that have been ridden for years. If you check the engine compression when the engine is new, you will be able to tell when it needs to be rebuilt when the compression goes more than 25% below what it started at. For all the symptoms that lead to a top-end needing a rebuild read more here.

The Most Common Reasons Why Your Dirt Bike Won’t Start:

  • Gas isn’t turned on/no gas in tank
  • Gas is old and varnished
  • Choke isn’t on/not working properly
  • Carburetor is dirty
  • Fuel injector is clogged/dirty
  • Air filter is dirty
  • Poorly tuned carb jetting
  • Battery is too weak
  • No spark
  • Spark plug is fouled
  • Faulty/broken kill switch
  • Intake air leak
  • Low compression

Put this cheat sheet in your garage for when your bike won’t start!

I want to give you this checklist as a FREE 1 page PDF that you can print and pin up in your garage so that you can refer to it any time your dirt bike won’t start. Click here to download it for free.

Blake Nowell

Sunday 17th of July 2022

I have a SSR 125 the chain got locked up on it the rear wheel stuck and it cut off and I haven't been able to get it to crank since I've got a new CDI box on it it's getting fire it's getting gas the kill switch is fine not sure what else is wrong any ideas

Andris

Sunday 5th of June 2022

i have 125cc lifan pitbike i rode it for 15m and gave it a big ol rev and it stalled. and doesnt start.

ivve cleaned carb. new sparkplug with spark. clean fuel. have oil. good compression. filter is good, spark plug is wet.

Kelley Fager

Monday 6th of June 2022

Hey Andris, so you need to figure out why the spark plug is wet. It may have gotten flooded from tipping it over or rich jetting. You can try holding the throttle wide open while you start it (then let go of throttle). Just be careful because this can push back harder on the kickstart lever.

Kim

Saturday 17th of April 2021

I have a Taotao DB10 pitbike, I broke the left handle bar switch when I was backing up my car I thought that was the reason it won't start. I replaced the whole kill switch with a new one but still it won't start. It's an electric starter and nothing happens when I press on the switch. Any ideas?

Kelley Fager

Saturday 17th of April 2021

Hey Kim, thanks for reading! Is there a safety switch/wire for the clutch that's not connected?

Octave

Thursday 8th of April 2021

I have a set 110 2020 and it won’t start. Carb had been cleaned air filter is clean has gas new spark plug but won’t start? Any ideas ?

Kelley Fager

Thursday 8th of April 2021

Hey Octave, did you confirm it has spark? Did it just start happening?

Kevin

Friday 12th of March 2021

Took off the whole top end and the piston rings were cracked. I am going to be ordering some new ones soon

Kelley Fager

Saturday 13th of March 2021

Yep, sounds about right. Just get a new top-end kit if the piston is scored. What about the cylinder?