The black rubber o-ring - does it go right on top (shortest part) or on the bottom?
(http://i.imgur.com/El73F.jpg)
Put the washers under the E-clip, then slide the white donut up. The donut keeps the washers from sliding off. Just had mine apart last night. The black o-ring goes up top under the black plastic carb cover. It sits in the indent on top of the carb and seals the little brass vacume line that leads from the carb throat to the carb sync port on top of the black cap.