Heat water in a large pot until simmering. Add 2 cups dandelion petals; simmer for 10 minutes. Remove petals with a slotted spoon and strain over a bowl; squeeze out as much liquid from them as possible. Discard petals. Repeat with remaining 2 cups petals.

Measure out 3 cups of dandelion-infused water, adding tap water to make up the difference if needed, and pour into a large pot. Add lemon juice, pectin, and yellow food coloring; bring to a rolling boil. Add sugar; return to a boil. Cook, stirring constantly, about 1 minute. Remove from heat and skim foam off the surface if needed.

Pour mixture into hot, sterilized jars, filling to within 1/4 inch of the top. Run a clean knife or thin spatula around the insides of the jars to remove any air bubbles. Wipe the rims of the jars with a moist paper towel to remove any residue. Top with lids and screw on rings.

Place a rack in the bottom of a large pot and fill halfway with water. Bring to a boil and lower jars, 2 inches apart, into the boiling water using a holder. Pour in more boiling water if necessary to bring the water level to at least 1 inch above the tops of the jars. Bring the water to a rolling boil, cover the pot, and process for 7 minutes.

Remove the jars from the pot and place on a cloth-covered or wood surface, several inches apart. Press the top of each lid with a finger, ensuring that the seal is tight. Let cool, about 24 hours.