Peel pears. Cut into quarters and remove stem and ends. Chop pears into small chunks.
Transfer pears, lemon juice, and pectin to a large stockpot.
Heat to a boil, stirring constantly. Pears will break down; should you have an immersion blender, you can blend them down a bit further, too.
After 10-12 minutes, fruit should be soft. Use an immersion blender or mash with a masher to smoothen out jam.
Stir in sugar; return mixture to a rolling boil. Boil for an additional 5-15 minutes, until the jam thickens and reaches a temperature of 220 degrees on your thermometer.
Once mixture reaches desired temp, ladle into into sterilized jars and fill to 1/2" of the top rim. Top with lids and bands, finger tip tight.
Process in water bath canner for 10 minutes; remove from water bath canner and allow jars to set (may take up to 48 hours).