Follow steps 1 through 4 of Canning Instructions, using five pint-size jars.
Meanwhile, stem, seed, and finely chop bell peppers; you should have 4 1/2 cups.
In an 8- to 10-quart pan, combine bell peppers, vinegar, lemon juice, chili powder, butter, and pectin. Bring to a rolling boil over high heat, stirring often. Stir in sugar; when mixture returns to a boil, stir for exactly4 minutes if using MCP pectin (1 minute if using Sure-Jell or Ball Fruit Jell). Remove from heat immediately.
Skim and discard any foam from jam, and stir occasionally for 5 minutes to distribute peppers evenly.
Follow steps 5 through 11 of Canning Instructions, leaving 1/4 inch of headspace in each jar and processing jars for 5 minutes (see Notes). For best flavor, let jars stand at least 2 weeks before opening.
Sunset's Canning Tips:
Add butter to jams and jellies to prevent foam from forming during cooking. If you omit the butter, skim off the foam before ladling jam or jelly into jars. The recipe will yield about 1/4 cup less.
Measure all the sugar into a bowl before beginning the recipe. Many canning recipes call for a large volume of sugar to be added when a mixture is already boiling; measuring ahead simplifies this step and prevents mistakes.
Use a ruler to measure volume. Some recipes call for a mixture to be reduced by a certain amount. To ascertain this easily, insert a clean, wood ruler into the pan before cooking and measure how far up the mixture comes. Then cook as directed until it has reduced by the percentage specified. For example, if uncooked mixture measures 4 inches in pan and recipe says to reduce by half, cook it down to 2 inches.