updated my other post with gas cap information as to why check valve changed
The fuel tank vacuun relief valve part of the check valve , was relocated to the gas cap in 1982.
79-81 gas caps do not have vacuum relief built in them therefore the 3-way type fuel check valve.
The 82-83 gas caps have vacuum relief valve added to them , therefore the newer check valve is only 2-way.
This also implies 79-81ZX fuel caps will not work on 82-83 ZX