Yamaha RA31/A, 1967-1968, 125 ccm 4-cylinder, aircooled/watercooled(A).

The RA31/A was the first V-four 125 ccm racer Yamaha ever made.

Bore x stroke were 35 x 32,4 mm which gave 124,7 ccm. The latest version gave 42 PS/16.500/17.000 rpm. Topspeed was 225 km/h! Gearbox was 9-speed and with the narrow tyres (front 2.50-18 and rear 2.75-18) weight was only about 91,5 kg. Carburetors wre 22 mm.

Yamaha RA31

This old drawing gives an idea of the complexity of this racer

Yamaha RA31, 125 ccm

And this close up shows definitely how skilful the mechanics had to be to work on these little jewels!

Yamaha RA31 125 ccm 1967