Checking, Measuring, and Adjusting Motorcycle Fuel Levels in the Carbs

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Carb floats control the fuel level in the carb bowls. The motorcycle shop manual will specify the correct fuel level for your bike.

An improper fuel level can cause all sorts of problems.

If your fuel level is too low, you might be running lean.

If it’s too high, you might be running rich and fouling your oil with gas.

Improper fuel levels in the float bowls can also lead to:

  • Difficulty starting.
  • Over flowing carbs and leaking gas.
  • Poor performance or cutting out at different throttle positions.

One of the best way to measure the fuel level is with the clear tube method.

How Measure the Fuel Level in the Carb Bowls using the Clear Tube Method

Refer to your service manual for the correct fuel level in the carb bowl. It’s typically a couple millimeters below the top of the bowl.

Motorcycle Clear Tube Fuel Measurement
Clear Tube Method for Checking Fuel Level in the Carbs

To measure the fuel level with the clear tube method:

  • Connect a clear hose to the overflow/drain hole in the carb bowl.
  • Put the bike on its center stand.
  • Make sure the carbs are level.
  • Loosen the drain screw.
  • Allow fuel to enter the clear tube.
  • Hold the tube up against the carb bowl and check the fuel level.
  • Measure the fuel level.

If the fuel level is too high or too low, you’ll need to adjust the float tab that sits above the float needle.

To adjust the fuel level, you’ll need to:

  • Unscrew the float bowl.
  • Remove the floats by pulling out the retaining pin.
  • Gently bend the tangs on the carb floats.
  • Make small and careful adjustments and re-measure.

Bend the float tab towards the float needle if your fuel levels are too high, this will lower them

Bend the float tab away from the float needle if your fuel levels are too low, this will raise them.

NOTE: This is a test that should not be performed on a moving bike. 

You can also do this after you’ve cleaned and rebuilt the carbs while they’re still off the bike. You’ll just need to prop them up so they stay level and you can access the drain plug and get gas to the bowls.