The English magazine "MotorCycleNews" showed this picture in their Wednesday, September 13th, 1967 issue. (It is similar to the bikes on the previous page!)The caption reads:

"This baby is a race winner"

"Yamaha latest baby, already well established in Japan, has proved itself a race winner. This racing version of the 100 cc YL-1 averaged 80,48 mph (128,84 km/h) to win a clubman's event at the famous FISCO circuit where it set a 100 cc class lap record of 83,68 mph (133,97 km/h) The bike which set up these record speeds, against keen opposition from Bridgestone, Honda, Kawasaki and Suzuki, was fitted with special cylinder heads, cylinders, pistons and carburettors. In its tuned form the Yamaha develops 18 bhp and has a topspeed of around 93 mph (148,89 km/h)"

MotorCycleNews Sept. 13th., 1967

(You can click for a larger print, sorry it is a scan from a newspaper magazine)