Place peaches and lemon juice into a non-reactive (non-aluminum) pot. While stirring, slowly add pectin. Let stand 20 minutes; stirring every 5 minutes to blend pectin with fruit. Add syrup and mix well. Add sugar and mix well. Cook over low heat until just warm to the touch, about 100 degrees F. Do not allow mixture to become hot. Pour jam into jars or other tight-sealing containers to within 1/2-inch of top. Cover and let stand at room temperature until jam sets. Once there, store in freezer until ready to use. Keep jam in the refrigerator once opened.
Note: 12-16 peaches, peeled and pitted, should yield about 4 cups when crushed in a food processor or blender. For easier peeling, mark a shallow X into the blossom end of each peach. Submerge in boiling water 3-4 minutes, or until skins just begin to slip away. Drain well, cool in cold water, and then slip of the skins.