Does the cap have the tank vent?
If your cap looks like this then Item number #2 is a foam filter for the breather in the cap. If it's not breathing foam might be plugged with dirt. Part Number 5S7657. But if your cap looks like this then filter for breather is #3 Kit number 350-7735.
The cap is the vent. Chased my 953C (2ZN) for quite a while when coworkers put unvented cap on. With a full tank and an unvented cap, as the fuel level dropped, the tank would squeeze shut enough to block the fuel level float from dropping, resulting in umpteen road calls.
Mine is the first one. Will check that foam. Thanks