That's a 4-stroke engine. If it were 2 stroke, boy that thing will be a blast! Hell with the emissions I say! Still it should be a pretty quick scooter.
single-cylinder horizontal 4-stroke with single-shaft distribution and overhead cams and side chain control with 4 valves.
Here's the link from the Benelli Site: Velvet Dusk 400 (click on 'Technical Specs').