For the fuel systems of the LPG vehicles, (1) The pipe structure inside the gas container is not appropriate, and therefore, when the temperature rises after the engine is stopped and the fuel pressure in front of the excess flow shut-off valve rises, restarting engine may cause the fuel to flow rapidly. If this occurs, the excess flow shut-off valve may be activated, in which case the engine might not start. (2) If unsuitable fuel is used, the pressure reducing valve inside the vaporizer may be exposed to high pressure and the vaporizer may lose air tightness. If this occurs, the fuel may flow too rapidly, so the excess flow shut-off valve may be activated, in which case the engine might not start.