Place chilies on a small baking sheet and broil 3 to 4 inches from heat, turning as needed, until chilies are charred and blistered all over, 10 to 12 minutes. Cool.
Remove and discard skin, stems, and seeds. Coarsely chop chilies.
In a 6- to 8-quart pan, combine mangoes, chilies, and lemon juice.
Mix pectin with 1/4 cup sugar. Stir into mangoes. Stirring, bring to a rolling boil over high heat.
Add remaining 3 3/4 cups sugar and stir until mixture returns to rolling boil. Stir and boil exactly 1 minute longer.
Remove from heat.
Ladle into clean canning jars to within 1/8 inch of top. Wipe jar rims. Set clean, flat lids on top. Screw on bands. Invert jars for 5 minutes, then turn upright.
Let cool at least 24 hours. Check seals by pressing firmly on centers of the lids. If a lid pops back, it's not sealed; store it in refrigerator.
