Yamaha TT-R90 Manuel D'atelier Du Proprietaire page 8

4. When transporting the machine in
another vehicle, be sure is kept
upright and that the fuel cock is
turned to the "OFF". If it should lean
over, gasoline may leak out of the car-
buretor or fuel tank.
5. Never start your engine or let it run for
any length of time in a closed area.
The exhaust fumes are poisonous and
may cause loss of consciousness and
death within a short time. Always
operate your machine in an area with
adequate ventilation.
6. Always wear a helmet, gloves, boots,
trousers, and jacket for motocross
riding.