Dave,
You should have one needle with a rubber tip on it and one without. If your carb has a brass inlet seat(where the needle fits into) you will use the rubber tipped needle and no rubber seat. If your carb has a "drilled or milled" seat oftimes with no brass insert then you need to install the plain needle with the rubber seat. Always install the rubber seat with the little groove facing away from you or the needle. Make sure it is in flat by using a flat drill bit end just smaller than the inlet to push the seat flat into the bottom of the inlet. The float should be level in either instance.
Scott Deaver: B&S Authorized Master Service Technician, June 2005