A single-cylinder two-stroke with the timing set incorrectly will easily run backwards. Dan Gurney manufactured a series of recumbent motorcycles called the alligator which are very collectible pretty much each one was different as he modified the design. He frequently used single cylinder engines. There is a famous ad for Montesa that shows Dan Gurney riding one of their 250 dirt bikes and jumping it, he's wearing dress slacks and dress shoes.
I got his autograph at Daytona or Sebring, I forget which. I also saw him race Formula 1 at Watkins Glen in the 1960s. He eventually developed his own chassis the Gurney Eagle which used a Harry-Weslake designed V8
Viva Montesa! (Popular ad of the day)