The sport of motocross experienced explosive growth in 1973 and motorcycle manufacturers sought to capitalize on the expanding market with all four Japanese manufacturers fielding factory-backed teams alongside their European counterparts.
[1][2] Karsmakers is credited with helping raise the level of American motocross by stressing the importance of physical fitness and machine preparation.
[2] 1973 marked a turning point in American motocross when Jimmy Weinert became the first American rider to defeat the then-dominant European riders in the Trans-AMA Motocross Series at Lake Whitney Ranch in Texas.
[3] As in the 1973 season, after the season-ending 500cc race on September 9, American riders competing for the AMA national championship continued to accumulate points counting towards the national championship while they competed in the 1973 Trans-AMA motocross series, which began on September 23 and hosted visiting European riders from the Motocross World Championship.
[1] Although Karsmakers was a Dutch citizen, he was competing under an AMA license so, he was listed as the "Top American" finisher in the Trans-AMA series.