Why Does My Dirt Bike Run Better With Choke On?

Sometimes a dirt bike of mine will only run when the choke is on. What does this mean?

I'll show you the most common causes and how to fix it. 

How The Choke Works

A choke is a mechanical device in the carburetor that richens the air-fuel mixture. It either limits the amount of air that goes through by blocking it with a valve, or opens a circuit that increases the amount of fuel that goes through. 

So, you need to figure out why your dirt bike needs more fuel or less air to run properly without the choke. 

Runs Better With Choke

A dirt bike that runs better with the choke on means that it's running too lean. 

Why Is It Running Lean?

There's a lot of reasons why your bike could be running lean. The most common are:

• Dirty carburetor
• Pilot or air/fuel screw too lean
• Float height not properly set
• Air filter dirty
• Timing is off (generally a 4 stroke problem)

Timing Is Off

Can timing on a 4 stroke dirt bike will throw everything off. If your bike doesn't run well just after rebuilding it, double check that the camshaft timing is correct. 

Dirty Air Filter

A clogged air filter restricts the amount of air that can go through to the engine. This can cause it to run lean enough to need the choke on to run. 

Check your air filter that it's clean and properly installed. Keeping the filter clean is just one of several important maintenance items that should be regularly checked or serviced. 

Float Height Incorrectly Set

Float height that is incorrectly set affects jetting. A low float height will cause a lean condition, which may require you to keep the choke on. 

Properly setting the float level is crucial before you making any jetting changes. 

Pilot or Air/Fuel Screw Adjustment

The pilot jet circuit mostly controls how your dirt bike starts, as well as 0-¼ throttle position openings. 

A pilot jet that is too lean may struggle to stay idling, this needing the choke to stay running. 

Even if the pilot jet is the right size, the air screw (2 stroke) or fuel screw (4 stroke) may need to be richened. 

The air/fuel screw is used to "fine tune" the pilot jet circuit. 

Dirty Carburetor

Does your dirt bike run with the choke only? There's a good chance that the carburetor is dirty. This is a problem I often see from using regular pump gas and letting the bike sit for months without running it. 

Usually it's the pilot jet that gets clogged from the gas breaking down, but sometimes I have to take the whole carb off and use my special cleaner. 

Cleaning the has always made a rough running bike run better. For a complete guide on how to clean your carb click here. 

Tune your air/fuel screw in just a few minutes!

Maybe you know your dirt bike needs the air/fuel mixture screw tuned but you're not sure how to do it or afraid you'll mess something up. I started out just like you, and I learned by taking one step at a time, and now I want to share with you how to easily tune it in just a few minutes!

Have a 2 stroke dirt bike? Click/tap here to learn how to adjust the air screw.
Have a 4 stroke dirt bike? Click/tap here to learn how to adjust the fuel screw.