Halve and stone the plums. Put the plums and measured water into a preserving pan and bring to a boil. Lower the heat and simmer, stirring occasionally for 30-40 minutes, or until the plum skins are soft and the fruit is extremely tender. It should have reduced by about one-third. Add the warmed* sugar, and stir over the low heat until the sugar has completely dissolved. Increase the heat and boil rapidly for about 10 minutes, or until it reaches setting point (104c). Remove from heat to test. Stir in the pecans. And immediately pour the jam into prepared jars. Seal and label.
*WARMED SUGAR*: Put in a roasting pan in the oven on the lowest setting. Warm for about 15 minutes. Sugar dissloves more quickly into the fruit if it has been warmed first.
