Chris Jones, of Bromsgrove, Worcestershire, had qualified for the front row of the 125cc British championship round on his Red Bull Rookies Honda. But his engine appeared to stall at the start, and other riders from further back collided with him.
The race was stopped, and Jones was flown to Hull Royal Infirmary, where doctors could not save him.
The age limit for the 125cc feeder class at British Superbike Championship meetings was lowered from 15 to 14 this year in an attempt to help youngsters graduate to world championship events sooner.
Their bikes have a top speed of about 140mph compared to the 200mph potential of the 1,000cc superbikes in the senior category. Jones, however, was almost stationary when his engine stopped.
"We have assessed his motorcycle, and there is no indication of any technical failure," Stuart Higgs, the race director, said.
"I don't believe that his age was a contributory factor. Chris was lying third in the championship, which shows how good he was."