[8] Benelli had only made 250 cc and smaller machines since WW2 and wished to expand their range, particularly into the lucrative North American Market which was dominated by British twins.

Development of the machine continued during this time,[5] including by Renzo Pasolini[9] and actor Steve McQueen, who was the US ambassador for Benelli.

[12] Following Alejandro de Tomaso's acquisition of Benelli in 1972, a revised version, the 650S, was introduced that had an electric starter fitted.

[13] To counter the effects of vibration, many components were rubber-mounted (silentbloc) and weights added to the handlebar ends.

It had a higher compression ratio[15] giving more low-end torque, further rubber-mounting of components, a humped seat and clear handlebar fairing.

[6] Organised by Milan dealer Lombromotori to demonstrate reliability, a S2 was run continuously around Italy for 25 hours by a team of 18 celebrity riders.

These included Bruno Francisci [de], Tarquinio Provini, Gigi Villoresi and Walter Villa.

The engine used horizontally split crankcases; o-rings on mating surfaces and external oil-lined were kept to a minimum.

[3] This was replaced by an electric starter on the S models, driven by a chain,[19] and an alternator fitted on the end of the crankshaft.