Four stroke engine with intake manifold

The present invention relates generally to a new engine for use in, for example, personal watercraft. In particular, the present invention relates to a new four-stroke in-line engine that was developed with a view to the future stricter environmental and emission regulations. The engine has a flexible intake manifold that can be configured for use either with a supercharged engine or a normally aspirated engine. Further, the intake manifold is configured such that a flame arrester is positioned therein to prevent the exit of flames from the manifold in the event of an engine backfire. The four stroke internal engine having an air intake system connected to the cylinder head and operatively connected to the intake passageway. The air intake system includes an air intake manifold having symmetrical construction with a central air passageway extending between a first end and a second end. At least one passageway extends from the central air passageway to a free end, which is operatively coupled to the intake passageway. The air intake system is usable for both a supercharged and normally aspirated engines.