The other innovation of the season was the brand new 250cc engine derived from the similar motocross model driven to victory by Leitgeb in 1970.
This model wasn't meant for mass production, but was a prototype developed by Graz specifically for racing and characterized by a enormous sand cast aluminum cylinder and an innovative cylinder head with straight rounded fins. The motorcycle was set up in Italy using a mass produced frame and given to Francesco Marini to compete in the Italian Championship.
Marini managed an excellent second place only a few seconds behind the Ossa of Carlo Rinaldi.
The Valli Bergamasche (1/2 June), known as the toughest race of the season, saw the Puchs in the front row, winning 1st place in the 100cc class with Wagner and 3rd place in the 125cc class with Dietrich.
In the 175cc division the German Lorenz Müller came 2nd, Mario Pedrali 7th and Gianluigi Sora 10th. As the cherry on top, the fearless Heribert Dietrich won the 125cc division at the Six Days of the Isle of Man (20/25 September).
The experimental motorcycle on which Marini raced in the Italian Championshipwasn't developed further due to the inadequate chassis, too fragile to withstand all the power which the 250cc engine was capable of producing, also a major consideration was the length of the races, which could not be compared to the much shorter motocross trails.
The many break-downs due to gearbox problems convinced the Graz technicians to rethink the design. Unable to design a new larger covering able to house a new hardier gearbox with six gears, they chose instead to reduce the ratio down to five, increasing the thickness of all components.
At the same time the power supply was adjusted to allow for the new ratios.
The many tests carried out during the season finally paid off when changes were carried through to the mass produced models in the same year.
