Man pleads guilty to setting Adelaide teen on fire in 'act of jealousy'

A young man has admitted he set fire to a teenager from Adelaide's northern suburbs, in what the victim says was an horrific act of jealousy.

21-year-old Joshua Lomas pleaded guilty to causing serious harm with intent to victim Luke Coburn. In return, prosecutors dropped a charge of endangering life.

The 17-year-old victim was sitting in his garage at Munno Para, when Lomas doused him in petrol and set him alight in January last year.

The victim believes it was over a girl he had started seeing.

Mr Coburn described his ordeal as "the worst thing anyone could ever go through".

"I'm pretty relieved, glad he's actually owned up to what he's done and done the right thing," he told 9NEWS.

Lomas will be sentenced later in the year. An accomplice is still being sought by police.