Fuel injection engine and motorcycle comprising fuel injection engine

A motorcycle comprising:

• a fuel injection engine including:
• an air-intake passage configured to guide air taken in from outside to a combustion chamber formed by a cylinder block and a cylinder head;
• a fuel injector configured to inject fuel to an interior of the air-intake passage, wherein a part of the fuel is injected from the fuel injector along a fuel injection center line;
• an exhaust passage configured to guide exhaust gases away from the combustion chamber;
• and
• a water jacket through which cooling water flows to cool the air-intake passage and the exhaust passage;
• wherein an inner wall of the air-intake passage has a crossing point where the fuel injection center line and the inner wall of the air-intake passage cross each other;
• wherein the inner wall of the air-intake passage has a fuel adhering region which is a predetermined region including the crossing point;
• wherein as viewed in a plane crossing an air flow direction in the air-intake passage and passing through the crossing point, the water jacket is configured to be provided in a location that does not include the fuel adhering region;
• wherein a portion of the water jacket positioned between the exhaust passage and the air-intake passage has a longer wall extending along the exhaust passage to cool the exhaust passage and a shorter wall extending along the air-intake passage to suppress cooling of the fuel adhering region;
• and
• wherein the water jacket extends along a circumferential direction of the air-intake passage from a region near one lateral end position of the fuel adhering region to a region near an opposite lateral end position of the fuel adhering region as viewed in the plane.