Measure peaches into a large kettle and add lemon juice. While stirring, slowly add pectin. Let stand 20 minutes; stir every 5 minutes to blend pectin with fruit. Add syrup and blend well; add sugar and blend well.
Cook over low heat until just warm to the touch about 100° F. Do not allow mixture to become hot. Pour jam into jars to within 1/2-inch of top. Cover jars at once. Let stand until jellied.
Store in freezer until ready to use. Keep in refrigerator once jar has been opened.Servings: 8 half-pints