TLAHUELILPAN, Mexico — Gerardo Perez returned Saturday to the scorched field in central Mexico where he’d seen an illegal pipeline tap burst into flames to see if he could recognize missing friends. He couldn’t. Only a handful of the remains had skin. Dozens were burned to the bone or to ash when the gusher of gasoline exploded, killing at least 71 people. Perez said he and his son bypassed soldiers and ignored warnings to stay clear of the geyser Friday evening in the town of Tlahuelilpan in Hidalgo state, about 62 miles north of Mexico City. “We’re stubborn,” he said.