The modern day Japanese "Autorace", a kind of speedway on tarmac, bears very little in common with conventional speedway, but that didn't stop Barry Briggs having a go on the tarmac ovals of Japan and even brought one of their unique racing bikes back to Britain. The bike used a 661cc, parallel twin HKS engine.
Formed in the early 70s by Hiroyuki Hasegawa, HKS (Hasegawa Kogyu Seisakushu, loosely translated as Hasegawa precision industries) produced high performance components for grand prix racing cars. In the mid-80s they began to produce twin and single cylinder motorcycle engines for use in Autorace machines. In 1988 HKS won the contract to supply standardised engines for Autorace.
Fueled by rumours of fragility and unreliability, the contract was terminated in 1992 leaving HKS with a surplus of unsold engines. An attempt was made to introduce them into American flat-track racing a few years ago, but all to no avail. Another attempt was made to have them fitted into 60s style café racers, Mick Hemmings had one on show at The International Classic Bike Show at Stafford a couple of years back, but who knows where the rest of them ended up.
At least one other HKS powered machine exists in Britain. Ian Paterson has a complete and beautifully restored 661cc single cylinder machine, to accompany his Kyokuto engine, at the Cinder to Shale Collection in Scotland.