Monster 659 Owner's Manual page 86

Release the lambda sensor cable (G) from the tab (H) on the
tank flange cover.
Warning
Before removing the flange cover (16), make sure the
tank is empty and position a rag to collect any spilt fuel.
Hold the fuel tank in a raised position and remove the flange
cover (16) by unscrewing the nuts (17).
G
H
E
fig. 80
16
17
fig. 81
85