Im not sure what A stock main is(200/210?)but with no airbox you would need at least A 300.The pilot should be fine for now,to change the mains pull the carbs out,take off the bowls and there they are in the center with A little number stamped on it.The pilots are right next to the main in the little hole,1/8in flathead screwdriver to remove.
EDIT....................Just seen you have stock pipes,so mabey A 240 or 250,I dont know.