Yamaha's four-stroke TT500 of 1976 was a fun bike but much more of a cow trailer than a motocross machine. Although companies like C&J and others quickly began making lightweight frames and hop-up parts for the TT, it never became a decent MXer until Sten Lundin, working with Torsten Hallman, had Profab build a lightweight frame to his specs. Fitted with a specially fabbed aluminum swingarm, Fox Air Shocks, and a Simons fork, this HL500 (Hallman and Lundin) tipped the scales at only 247 pounds and had nearly 11 inches of travel front and rear. Bengt Aberg raced the 1977 500cc World Championship on an HL500, even winning a moto at the Luxembourg Grand Prix. Fun fact: Yamaha never supported the project, but the European team boss had Norton build 200 Aberg Replica bikes. In the US, Profab built a similar number but only as kits. The HL weighs less than a new WR450F! Want!

Sweden's Bengt Aberg, on the four-stroke Yamaha HL500 (no. 32), lines up next to Roger DeCoster on the factory Suzuki.

Yamaha HL500.

Aberg TT500 racing start.

Bengt Aberg race action.