there is a small square plug toward the back of the chain case to drain it with, you fill it by pulling the plug out of the top, like you were taking the top gear off, if you are studded, i would not run the track crazy loose, just set it up normal tension, the carbs are a pain in the ***. yes you need to pull the secondary witch means you need to pull the whole jackshaft on the xp, to sum it up...if you don't have the tool to pull the jackshaft, you need to pull the chaincase cover off anyway, so thats the way i would do it if i was you, pull the cover off, remove the top gear,remove the bearing retainer on pto side of the jackshaft, CARFULLY rubber mallet or put the bolt back in and tap out the jackshaft to get at the carbs...good luck man !!!
Win if you can, lose if you must, but always cheat...at least i'm honest about that !!!