Cut each pork tenderloin crosswise into 6 pieces. Press each piece, cut
side down, to form a round, about 1 1/2 inches thick. If end pieces are
thin, coil into round fillets; secure with toothpicks. Place rosemary and
thyme sprigs in nonmetal dish or heavy-duty resealable plastic bag. Stir
in vinegar and oil. Add pork, turning to coat with marinade. Cover dish or
seal bag and refrigerate, turning pork 2 to 3 times, at least 1 hour but
no longer than 24 hours.

Brush grill rack with vegetable oil. Heat coals or gas grill for direct
heat. Remove pork and herbs from marinade; reserve marinade. Place herbs
directly on hot coals. Immediately cover and grill pork 4 to 5 inches from
medium heat 7 minutes, turning and brushing frequently with marinade.
Discard any remaining marinade. Cover and grill pork 6 to 8 minutes
longer, turning frequently, until slightly pink in center. Remove
toothpicks.