yeah. what they said. 14/15 bing, 15 intake, and match the intake to your cylinder. make sure you have the right needle too, some have 1 little notch, others have 2.
you should be able to score a 14mm on the buy sell forum for not too much.
also, while you are matching that intake, match your exhaust, and widen the port a little. stay at least 1mm away from the ring stops. widening the exhaust port works wonders on stock cyls.