Conversation so far:
Where was Piquet born?
Piquet was born in Rio de Janeiro, then the capital of Brazil.
Was he interested in racing or races as a child?
Piquet started kart racing at the age of 14.
Did he race with friends or was there a race for kids?
Upon returning to Brazil, Piquet and three friends brought a 20 hp cart and participated in Brazilian go-karting (1971 and 1972 national champion.
How long did he race with the 20 hp cart?
CANNOTANSWER.

Question: What did he do after the 1972 and 1972 national championship?
Self-contained rewrite: What did Nelson Piquet do after the 1972 national championship?