In a large pot, cover yams with cold salted water.
Bring to a boil.
Simmer until slightly resistant when pierced (about 20–25 minutes).
Place in large bowl of ice water to stop cooking.
When cool, drain.
Peel yams and quarter lengthwise.
Whisk together lime juice, salt, and pepper, and add oil in slow stream, whisking.
Whisk in cilantro.
Taste to adjust seasoning.
Heat and lightly oil grill.
When hot, place yams on grill, uncovered.
Turn when grill marks appear, about 2–3 minutes.
Repeat on each side. Yams can also be cooked on an oiled-ridged grill pan over moderate heat, turning when grill marks appear and just tender.
Serve yams warm, drizzled with dressing.
Garnish with lime quarters and reserved cilantro sprinkled on top.