Honda BF9.9A Owner's Manual page 44

4. Remove the clamps used to close the fuel tubes. Connect the fuel
tank line to the motor. Turn the fuel tank vent knob to the ON
position, pump the primer bulb, and check for leaks.
NOTE:
If loss of power or hard starting is found to be caused by excessive
water or sediment accumulated in the fuel filter, inspect the fuel tank.
Clean the fuel tank if necessary.
42