You got it brand new? Still under 6 month warranty? You have the stock gas tank cap with stock vent hose?
Did it do it when it was bone stock? If so it is the dealer's problem. Put it back to stock and if it still does it take it to the stealership.
2018 YFZ450R SE : warning labels removed, TMD case saver, GYTR aluminum frame skid with the bracket mod, thick helicopter tape here and there, some stickers, everything else stock stock stock like the dealer likes it.
PIN IT PIN IT !!! SCREW BREAK IN STEPS.
On deck.circle: VORTEX ECU/PEAK RACING MOUNT - YOSHI SLIP ON NO SPARKY.