part # 8VO-14118-00-00. you need 4. expect to pay around $5 each. any yamaha dealer or online parts provider will have them.
i have posted the correct location several times, but for a refresher, with the carbs upside down and the airbox side facing your belly, the left and center pilot tubes get the caps. the right side remains open.
just so you dont get confused, the larger round parts of the carbs are the airbox side, the smaller sides go to the intake boots.