Rinse the kumquats and remove any stems. Slice the ends off of each kumquat and discard.
Cut each kumquat in half and carefully cut out white pith and seeds; discard.
Chop halved kumquats and pulp coarsely; place into a food processor along with the chopped orange. Pulse until the kumquats are chopped more finely and somewhat liquefied.
Measure the mixture at this point and pour it into a bowl. Add equal amounts of sugar to the kumquat mixture (ie. 2 cups of kumquat mixture will need 2 cups of sugar). Mix in sugar and add 2 tablespoons lemon juice.
Microwave on high (uncovered) for 6 minutes, giving the mixture a chance to boil.
Stir, and continue to microwave in 2 minute bursts (stirring after each burst) for a total of 10 minutes.
Remove from microwave, stir and let cool at room temperature. The marmalade will thicken as it cools.
Keep marmalade in an airtight container; refrigerate for up to 2 months. Freeze for up to 6 months.