This is not it's primary function. The overflow hose is not there to channel away excess fuel if you're in an overflow situation at the pump, clearly the gas pump can dispense fuel faster than a tiny hose is gonna allow it to escape. In that case you're in $hit
.
The overflow hose is there to handle overflow due to fuel expansion. So for example.... if you - even carefully without spilling - filled your tank to the very top and then.... left your bike parked in the sun, the fuel would expand and since you've left no ullage volume available (coz of your just-filled-it-all-the-way activity) the overflow hose allows the expanding fuel to escape. I have actually done this, and I can tell ya that quite a constant dribble of fuel runs outa there and (more or less safely) onto the ground beneath the bike. Imagine the outcome if you didnt have the overflow hose attached, where would the expanding fuel end up then??
It must have come out of the vent side, as the filler cap seals airtight. The only way the overflow hose can function is if the filler cap is left open (or bursts open, in which case petrol will spray everywhere anyway).
Regardless, it may still be a valid reason to keep the
vent (red nipple) hose on. Out of curiosity—how cool can metal be and still ignite petrol?
