Motocross history is filled with examples of creative ideas that were heralded as groundbreaking, but, because of the rapid rate of change in development, sank into the swamp of forgotten technology. Although some are best left abandoned, others were truly innovative (if not ultimately successful). MXA loves to reveal motocross’ tech trivia. Do you remember this idea? The Knox Box airbox?

Modern motocrossers lack the creativity of riders from the 1970s. Back in the day, when a racer had an issue with his bike he went out in the garage and invented a solution. Such was the case with AMA National rider Dewitt Knox, III. When the throttle stuck on his 1973 Yamaha YZ250A at the Lake Whitney National because dirt got past the minuscule Yamaha air filter, Dewitt’s dad decided that the YZ needed a bigger and better air filter, but there wasn’t any room for it with the monoshock in the way.

Dewitt Knox III’s Yamaha YZ250 with the Knox Box on the back.

Undeterred, Dewitt, Jr. cast a plaster of Paris mold of a remote airbox to fit on the rear fender. From the mold, he made a fiberglass airbox to hold the air filter up and away from roost and dirt. A 3-inch flex hose ran from the fender to the stock airbox. If it was muddy or dusty, Dewitt raced with the air filter in the Knox Box. If the dirt was good, he ran the stock Yamaha filter but with the air coming from the empty Knox Box.

DeWitt ran the Knox Box on his YZs in 1973-1975; then, when he switched to Husqvarnas in 1976-1977, his dad made a new one for the Swedish bike. DeWitt scored several top-20 National finishes and won the 250 Support class at the 1975 Cycle-Rama 125 National in San Antonio.


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