De Bosscher started in races on the road as well as on the track , but was more successful on the track. Several times he took podium places at Belgian rail championships in various disciplines. In 1977 he was two-time champion in the sprint and in the standing race . In addition, he started in 147 six-day races, four of which were won by “gekke Willy”, who was popular with the six-day audience for his funny inserts.
In connection with rumors about alleged motor doping in the summer of 2010, the Danish cyclist René Wenzel reported that De Bosscher had won the elimination round of the six-day race in Grenoble in 1979 on a “Vélo à moteur”. When the other drivers found out, she wanted to beat him up, which the Belgian six-day star Patrick Sercu prevented. It is possible that the “six day clown” De Bosscher thought this use of a motorized bicycle was a “joke”.