Carb Jets

Motorcycle, snowmobile, dirt bike and ATV carburetors have multiple jets and fuel conduits. Why so many carb jets, needles, etc? What do they do?


Carb pilot jet examples

Pilot or Slow Jet

Pilot jets are responsible for fuel delivery during start-up, idling and low RPM range engine operation. This is the jet to check if your bike has trouble getting fuel when starting, has a rough idle or stalls at low RPMs.

The photo on the right shows three styles of pilot jet.

Main Jet

Controls fuel delivery in mid to top range of RPMs. Installing larger main jets will also supply more fuel to eliminate top end surging.





Carb Fluid Needle Examples

Fluid Needle

The fluid needle is responsible for mid-range RPM fuel delivery.

Adjustments to the fluid needle will improve throttle response on acceleration and deceleration. Adjusting the needle will also assist in the elimination of back firing.

Float Needle

The float needle, in conjunction with the carburetor float, controls the flow of fuel from the gas tank into the carb.

When the float goes down, the needle allows gas in, filling the bowl to a specific height.

The rising float lifts the float needle into the needle seat, sealing off the gas entry point.

Carburetor Float Needle and Valve Assembly

When a carburetor float needle gets corroded or fails for whatever reason, it can no longer move freely in and out of the needle seat.

It can get stuck outside the seat, effectively, in the open position. This allows gasoline to overfill the carb and run down into, and flood, the engine.

Or it can be stuck in the seat or the closed position. In that case the fuel can not reach the bowl.

The photo on the right shows a new float needle and needle seat, also called a float valve assembly.



Return from Carb Jets to Repair Advice Q & A pages

Return from Carb Jets to Need to Know page


Ask us a question using the form below. Please include your machine's year, make and model as well as any customization of the bike {ie aftermarket exhaust system, air filter, etc}.

Why do we ask for your state and country? Prevailing climate and altitude makes a big difference.

For example: If you have your ATV tuned by a shop in the Catskill Mountains (1600-1900 feet above sea level) and it runs great! Then you take it home to the Jersey shore & suddenly it won't stay running. Don't blame the shop. They tuned it to perform well in the thinner, drier atmosphere of the mountains, not at sea level.

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