That hose runs up and slips under a metal tab on top of frame rail. just a breather and needs to be above carby.
Could also just slip into the frame, same on all the honda's I have had.
Start here:
Air Cleaner Housing Removal/Installation; Carburetor Removal; Throttle Valve - Honda XR80R Service Manual [Page 72]
Honda XR80R Manual Online: air cleaner housing removal/installation, Carburetor Removal, Throttle Valve. Ti?Wiiiih Gasoline Is Extremely Flammable And Is Exploi'',E Under Certain Conditions. Keep Out Of Reach Of Children. Throtile Valve L Oosen The Ca Rburetor Lop. 5-4 Service. F Rom...www.manualslib.com
You , had a Honda ?