How To Easily Adjust & Set The Float Height On A Dirt Bike Carb

Need to know how to adjust the float height on your dirt bike carb? Whether you have a dirt bike that’s running poorly or you simply want the best performance, this article is for you!

I’m going to show you what the float is and does in your dirt bike, whether it’s a 2 stroke carb or a 4 stroke carb, why it’s so important to check and set the float height, and how to easily do it.

What does adjusting the float height on a dirt bike carburetor do?

Adjusting the float height changes the level that the fuel sits in the float bowl of your dirt bike's carburetor. This is simply controlling the amount of gas/fuel that sits in the carb before going through it to get burned in the engine. 

As the fuel gets used, the float level goes down. The float is connected to the needle and seat, and once the float gets low enough, more fuel comes in past the needle and seat. 

As the fuel level rises, the float level goes up and pushes the needle back up against the seat, shutting off the flow of fuel into the carb. This is a constant process as you ride because you're using different amounts of gas as you twist the throttle. 

Why is it so important to set the float height?

The float height is so important because it controls the amount of fuel in the bowl of the carburetor. 

If the level is too high, you'll have negative symptoms, such as fuel leaking out the overflow hose. Too low of a float level will also have negative symptoms. 

Why does the float height change?

When your dirt bike comes new from the factory, the carburetor should already be properly set up with jetting that's close to perfect (at least on most motorcycles). Therefore, there's usually no reason to adjust the float height unless you have jetting problems. 

However, the float height might change over time due to a couple of reasons. The part that controls the level may get worn out, causing it to move, or it may get accidentally bumped when taken apart or trying to put the float bowl back together. 

It’s a very small metal ‘tang’ or flange, and all it takes is a little nudge to change the float height.

Does float height affect fuel mixture & jetting?

Yes, the float height definitely affects the fuel mixture and jetting because the jet circuits rely on the level to suck in the fuel. If the float height is lower, then all of the jetting circuits (pilot, needle, main) are going to be leaner because there the fuel is further away and harder to get sucked through.

If the height is too high then the fuel is too close to the jets, causing too much fuel to go through and making it a richer fuel mixture. This is why it’s so important to make sure it’s properly set before you make any jetting adjustments or else you’ll be chasing your tail.

Does float level affect idle?

Yes, the idle can be affected by the float level if it's too high or too low. When it's too high, the idle may be slightly lower because the fuel mixture is richer, and vise-versa. 

With that said, the pilot jet circuit, air/fuel screw and idle screw have a bigger effect on the idle of your dirt bike. 

How does float level affect performance?

A properly set float level is not only easier to jet, but your dirt bike will be abe to perform better when it comes to predictable throttle response and power. 

What happens if the carburetor float is too high?

When the float level gets too high, the jetting gets richer because the fuel mixture increases. This not only loses performance, but you get negative symptoms, such as hesitation, gas leaking out the overflow hose and spark plug fouling. 

How do you test a carburetor float?

Whether you have a cork float, brass float or plastic float, they can all develop a problem that causes them to absorb fuel and sink. When that happens, the fuel level goes away high and there's no consistency. 

To test a float, you have to remove it from your carburetor. Simply put it in a bowl of water and let it sit overnight. 

If there's a pinhole that you can't see or the material is porous and absorbing the liquid, it will eventually sink. A good float will always float at the top of the water or fuel. 

Carburetor float level symptoms

Like most jetting problems, an incorrectly set float will usually have symptoms to let you know there’s something that needs attention. Here are some practical things to look for.

Carb float level too low symptoms:

• Hard to start your dirt bike (especially when cold)
• Bogging on acceleration
• Handing idle (RPM is slow to settle down to an idle)
• Power surges

Float level too high symptoms:

• Fuel leaking out the carb overflow hose (when you lean your dirt bike on its stand)
• Hesitation on acceleration
• Poor throttle response
• Lacking overall power
• Fouling spark plugs

How do you adjust float height?

Whether you have a Mikuni carb or a Keihin carb, adjusting the float height is basically the same. There’s a small metal “tang” that rests against the needle. To adjust the level, simply bend the tang and then check the float level.

You can do this easily with your hand - so easily that you should be careful because it doesn’t take much pressure to bend it! Make a small change and then check the float level and repeat until you get it properly set.

How do you measure float height?

Refer to your OEM service manual for the most accurate float height settings. With that said, you can get it really close by rotating your carb to a 45-degree angle from upside down - the float should be roughly parallel with the carb body surface.

Here are the simple steps to checking a dirt bike carb float height:

• Rotate the carb so that the float is pointing towards 3 o'clock - the pin and needle should be on top with the float hanging loosely
• Slowly rotate the carb up (towards 12 o'clock)
• Once the float stops (the weight of gravity), that's where the height is set - the carb will be close to a roughly 45-degree angle and the bottom pointed between 1 & 2 o'clock
• If you rotate all the way to an upside-down position, this can give a false reading because the weight of the float drops it even more, making it look like the float height is too high as seen above (carb reading is upside down)

How to make your dirt bike safer and more reliable

Jetting is one of the best ways to make your dirt bike run better, last longer, and go faster, but there are other things that riders neglect that will eventually cause problems.

I want to show you 3 easy ways to make your dirt bike last longer and help prevent a catastrophic failure that could leave you broken down and stranded. Click or tap here to learn more.