Kawasaki Motorcycle test
Rules, to the chagrin of those who write them, rarely work when their main reason for existence is social engineering. Racing, whether cars, bikes, boats or planes is resplendent with social rules. By social engineering we are not talking about what color clothes you're allowed to wear (although for years the AMA had rules requiring white pants in the pits and banning solid black leathers) or affirmative action at the AMA. No, social rules are those designed to bring more equality among competitors (even if they aren't equal). NASCAR is the most famous for this, they give a 1/4 of air dam and take a 1/4 of spoiler to try and make all brands equal on the track. Even in horse racing, jockeys have to wear weights to guarantee that every horse carries the same load.
Motocross has experimented with social rules for years. Perhaps the most famous of all the equality attempts was the claiming rule. The claiming rule was written to keep a racer, team or manufacturer from spending too much time, money or effort in building a world-beater bike -- because if they did, any competitor (in the same race) could lay down $3500 and buy the bike. It's a very esoteric concept of equality -- the belief that the bikes will remain fairly equal because they could change hands at the end of the day. It is great is theory, but the first time a privateer claimed a factory Honda CR250 (and drove away with it) all the factories threatened to pull out of racing. Seven days after John Roeder claimed Marty Tripes 1978 Honda, the claiming rule no longer existed. It's no surprise that spineless officiating does little to encourage equality.
Perhaps the best social engineering in motocross was done in 1973 to keep Suzuki from driving the European manufacturers out of the sport. A short time after entering Grand Prix racing, Suzuki was fielding 187-pound 250's and 202-pound 500's that demolished the competition in the hands of Joel Robert and Roger DeCoster. Cubic dollars, which the Japanese had from the early 70s street bike boom and Husqvarna, Maico, CZ, Bultaco and CCM didn't have (they didn't make street bikes), were calling the shots. The Euro manufacturers whined that they couldn't compete, so the FIM instituted the weight rule. Rather than wait for the European bikes to get their weight down, the FIM decided to bring the weight of the works Suzuki's up.
Starting in 73, 250cc bikes had to weigh more than 198 pounds and 500s could weigh no less than 200 pounds. The effect was immediate. Suzuki didn't have time to develop all new bikes for the 73 season, so they poured molten lead into the frames of Roberts RH250 and DeCosters RN370 to bring them up to the new weight limit. Joel Robert, claiming that the lead ruined the handling of his featherweight Suzuki, lost the 250 World Championship (after winning it for five straight years). Roger DeCoster fared better, he edged out Maico-mounted Willi Bauer for the third of his five World Titles. It seriously affects the handling of our bikes, says DeCoster. The bike had already been built when the weight limit came down. The factory had no choice but to add weight wherever they could.
Almost 25 years later the weight limit is still in effect (although Team Honda and Ricky Johnson dodged the scales twice with bikes that were underweight without incurring any penalty). Under 2000 AMA rules the minimum weight for a 125cc bike is 194 pounds and a 250 is 216 pounds. The bikes can be weighed after a race at the AMA's discretion. For weighing, the gas tank must be empty (although the radiators can be full). Ballast of any kind (like the lead that Suzuki poured in it frames in 73) is illegal.
Historically, the only championships that could claim to have been affected by the FIM/AMA weight limits were those inaugural ones in 73. Joel Robert might have been a seven-time 250 World Champion except for social engineering to save the European motorcycle manufacturers pride. Did the weight limits save them? No. All of the major Euro players from 73 are out of business today, and in the 25 years since European manufacturers only won ten of the 40 FIM crowns awarded.