My Dirt Bike Won’t Idle – How Do I Fix It?

Dirt Bike won’t stay running after you got it started? Maybe you can’t even get it started. Whether it runs great or it runs rough after starting it, there’s many reasons why your dirt bike won’t idle properly. If that’s you right now, you’re in the right place. 

À 2 stroke or 4 stroke that won’t stay running is actually a fairly common problem. Some causes are very easy and quick to fix, but some bikes require a little more investigating to solve the real issue.

In this article we’ll cover every common problem that causes a dirt bike to not idle, as well as the less likely issues in case you’ve already tried everything else.

Here are the top 13 reasons why your dirt bike won’t idle:

  • Idle set too low
  • Engine isn’t warm/didn’t leave choke on long enough
  • Fuel/air screw needs adjustment
  • Pilot jet too large
  • Pilot jet or circuit is dirty
  • EFI injector is dirty
  • Dirty air filter
  • Fuel filter clogged/line kinked
  • Float level set too low
  • Air leak
  • Reeds are worn out (2-stroke)
  • Carburetor is worn/broken internally
  • Stator is bad

Don’t Touch Your Bike…

Before you get started, there’s a couple things you should know. The first tip is to only do one thing at a time. If you’re messing with multiple things, you’re a lot more likely to cause even more problems.

In the event that you do fix your problem, if you did 2 or 3 different “fixes”, then you may miss out on a “learning experience”. 

The second tip is to always start with the easiest thing, then work your way to more involved ways to identify the root problem. Why would you start with the most difficult and time consuming option? Save your time and money and pick the easiest thing to check first.

Are 2 Stroke Dirt Bikes Supposed To Idle?

The simple answer is “Yes”. All dirt bikes, both 2 and 4 stroke and made to be able to idle for a reasonable amount of time. 2 strokes may have a more erratic idle just because of the way the engine works and the timing of each power stroke. 

A 2 stroke that doesn’t idle for more than 30 more than likely has the idle set too low or the jetting needs to be corrected.

Idle set too low

Whether you have a 2 stroke or a 4 stroke, if the idle adjustment is set too low, the engine won’t stay running. Turn the idle screw in and see if your dirt bike stays running. You may have to turn the idle down slightly as the engine temperature warms up.

Did You Warm The Engine Up?

Some dirt bikes, especially older models, are more cold blooded. This means that it takes longer for the engine to fully warm up to operating temperature.

New fuel injection dirt bikes will automatically compensate and richen the fuel mixture to keep the bike idling, but carbureted bikes require a little more manual effort. 

Why You Need To Use The Choke

A cold engine needs a higher fuel/air mixture in order to run because it’s harder to burn efficiently at lower internal temps. As there engine temps rise, less fuel is required to keep it running.

This is why some dirt bikes need to have the choke on left longer to keep them running without needing to give it more gas by twisting the throttle.

Fuel/Air Screw Needs Adjustment

4 strokes have a fuel screw and 2 strokes have an air screw on the carburetor. They both perform the same type of function, but in opposite ways.

The purpose of the fuel/air screw is to fine tune the adjustment of the pilot jet circuit. This circuit most affects starting your bike as well as throttle response and power from 0-¼ throttle inputs. 

Properly jetting a carb is important if you want the best throttle response, power, and fuel efficiency possible. To learn more about why and how to jet a dirt bike carb click here

Pilot Jet Is Wrong Size

This is the next step if the fuel/air screw adjustment didn’t fix the idling problem. A pilot jet that is too big gives too rich of a mixture that there engine can’t fully burn.

You may be able to get your bike started, but it will have a hard time staying running. Going leaner/smaller on the pilot jet may cure the problem and get your bike to idle properly again.

Pilot Jet/Circuit Is Dirty

A dirty carb, and more specifically, a dirty pilot jet circuit is one of the most common reasons why a dirt bike won’t stay running. Other common signs of a dirty carb:

  • Hard to start
  • Bogs or runs rough
  • Only runs on choke
  • Backfires
  • Low/or hanging idle
  • Lack of power

A carburetor gets dirty because it sits for a period of time. If fuel is left sitting in the carb then it will deteriorate and start to gum up after a while.

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

This is especially true with cheap regular pump gas with high amounts of ethanol. Running a high quality gas, such as a non-oxygenated had with no ethanol, will last much longer before breaking down and causing problems in your gas tank or carb. 

EFI Injector Is Dirty

A dirty or clogged fuel injector can also cause engine running problems. If your fuel injected dirt bike won’t idle or stay running well after sitting for several months, try running some fuel injector cleaner through it.

Sometimes just running an engine for a little bit will clean out the junk that was sticking in the fuel system. 

Dirty Air Filter

An air filter that isn’t regularly maintained will build up dirt and other foreign materials on it over time. The filer is there to prevent these objects from entering the engine. 

Dirty Air Filter causes spark plug to foul
Dirty Air Filter After Riding In Sand

But if the filter is so dirty then it won’t allow enough air through the carb/throttle body. This creates a rich air/fuel mixture, similar to what a pilot jet that’s too large causes.

If your air filter hasn’t been cleaned or replaced within your last few rides, it needs to have a fresh air filter installed.

Fuel Filter Clogged/Line Kinked

Adding a fuel filter inline with the gas line can be a great way to help prevent any sediment or foreign materials from entering the carb or fuel injector. However, if the filter has collected so much sediment and junk in it, not enough gas will flow through to the fuel system, making the engine run rough.

If you can see the filter is dirty, replace it and test your results. Also check for a Kinked fuel line. The line from the gas tank to the carb/fuel system will rarely be straight, but it should never be kinked or or pinched. This will also not allow enough gas to reach the fuel system.

Float Level Is Off

Proper float level is critical to the jetting. If the float is set too low for then the engine will starve for fuel. A float level that’s too high will often flood over and gas will spill out the overflow tube. If your float level (also known as float height) is not correct, your dirt bike will run poorly. 

Check your OEM service manual for the float level specs. It’s not very difficult to adjust the level. You just need to remove the float bowl, either by rotating the carb or removing it from the intake boot to get access to the float bowl. 

This float looks to be slightly high and should be adjusted.

Once the float bowl is off, remove the float pin and float, then carefully adjust the metal “tang” in the proper direction to get the correct float height. Re-install everything and see if that solves your problem.

Air Leak

A pesky air leak will most certainly cause problems. Not only can your engine run poorly, but a leak will allow dirt and other materials to more easily enter the engine. This will greatly reduce the engine life. Dirt is an engine’s worst enemy, which is why it’s so important to keep your air filter clean if you want an engine to last as long as possible.

If you don’t visually see any gaps or cracks in the intake boot or box, there’s an easy way to test for air leaks with the engine running. Spray a little bit of a flammable substance (such as carb/brake cleaner) around the intake boot.

If you notice the RPM drop or rise, then you most likely have an air leak. A part or bolt is either too loose, cracked, or a gasket needs to be replaced.

Reeds are worn out (2-stroke)

Although not as likely, the reeds on a 2 stroke can cause idling problems. The reeds aren’t much harder to remove than the carb.

Once you have the reeds cage off, visually inspect the reed petals. If you hold it up to light and there’s a gap, then the petals are worn and should be replaced. 

Carburetor Is Worn/Broken Internally

Sometimes there’s just no other explanation than that the carburetor itself is causing the problem. Whether your dirt bike won’t stay running, or it runs rough, internal wear or damage can wreak havoc on your riding time. 

In an attempt to save money, find the same bike as yours with a known working carburetor. If you’ve tried every other jetting change, swap your carb with it and see if your problem is fixed. Yes? Then replace the carb and get back to having fun riding again.

Stator Is Bad

A faulty stator is another less common problem, but still occasionally happens, and that’s why we’re covering it here.

You may be able to get your bike started with a bad stator, but it won’t be able to charge and power the electrical system and/or battery. 

How To Test A Dirt Bike Stator

A way to test your stator is to use a voltmeter. Check the voltage of your battery with the engine and power off. It should check around 12.5-13 volts. If it’s lower than that, your battery needs to be charged or possibly replaced.

Start the engine and check the voltage at the battery again. Rev up the engine RPM and you should see the voltage increase above 14 volts. If the voltage does not increase then the stator is not charging the battery. This either means that the stator is bad, or that you simply have a poor or missing electrical connection/ground.

Kelley Fager

Kelley started riding a Honda 50 at the age of 6 years old. The passion for dirt bikes started there and grown into a lifelong pastime of riding and learning how they work. Motocross Hideout is the result of sharing his past, present, and future knowledge and experience.

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