1. Disconnect the tubing from the 2-way valve side and the carbon filter side, connect a hand vacuum pump to the carbon filter, create a vacuum and check that air is passing through.
2. Check tubing for damage and loose connections.
Checking the 2-way valve
1. Connect a hand vacuum pump to the 2-way valve on the side of the fuel tank connection, create a vacuum and check that air is passing through.
If no air is flowing or the valve itself is leaking, replace the 2-way valve and retest.
2. Connect a hand vacuum pump with the air pressure side to the 2-way valve on the fuel tank connection side, pressurize and check that air is passing through.
If no air is flowing or the valve itself is leaking, replace the 2-way valve and retest.