ENGINE SYSTEM AND STRADDLED VEHICLE

During start-up of an engine, an engine unit is controlled to perform a reverse rotation start-up operation. In the reverse rotation start-up operation, a fuel-air mixture is introduced into a combustion chamber while a crankshaft is rotated in a reverse direction, and the fuel-air mixture is ignited such that the crankshaft is driven in a forward direction. In the reverse rotation start-up operation, an ignition threshold value is set based on a first parameter corresponding to friction of the engine, and the fuel-air mixture in the combustion chamber is ignited when a second parameter corresponding to pressure in the combustion chamber reaches the set ignition threshold value.