Ok - let's try something else ....
For 3.5 lbs of grapes .... (will make about 4 half-pints of jelly)
JUICE: crush the grapes in a pan, add 1 chopped apple (skin, core, seeds, and all) and 1/2 cup water. Cover, bring to a boil, then reduce to a simmer and cook 10-15 minutes. Strain through a wet jelly bag or cheesecloth. You should wind up with 4-cups of juice.
NOTE: The apple will supply your pectin. If you use 1/4 firm ripe and 3/4 fully ripe Concord grapes you probably could get away without the apple ... but humor me and use it. I don't know what kind of grape you're using.
JELLY: Measure your juice - it should be 4 cups. The amount of sugar that you need is 3/4-cup sugar for each 1-cup of juice. So, for 4-cups juice you need 3-cups sugar.
Get your jars and canner ready and place a salad plate or saucer in the freezer, get a glass or cup of COLD water and a metal tablespoon ready (put the spoon in the cold water to chill it).
NOTE: the next part can take anywhere for 10-30 minutes, or so.
Put the juice in a large saucepan, add the sugar, stir until dissolved. Bring to a boil and stir constantly until the mixture is to the gelling temperature (about 9-10 F above the boiling point of water where you live) - generally about 220-222 F at sea level.
Temperature doesn't always guarantee you are at the gelling stage. Dip a cold tablespoon into the jelly and check to see how it comes off the edge of the spoon when you pour it out. When the jelly has reached the gelling stage it will pour off the spoon in a wide sheet, instead of individual drops. When you reach that stage - remove the pot from the heat - take the plate out of the freezer and pour a tablespoon of jelly on it and stick it back in the freezer for a minute or two (to bring it quickly down to about room temp). If it sets up - your ready to proceed with canning it. If not - cook it a little more until it is done.
POSSIBLE PROBLEMS:
1. Liquid and Powdered pectins are NOT interchangeable.
2. Sugar substitutes are NOT interchangeable for sugar.
3. FOLLOW THE RECIPE you are using EXACTLY!
Hope this helps.
Michael