Most probably you need to add a little yeast nutrients, and as posted by PM above, do you know the gravity? Sometimes when yeast dont have enough nutrients they produce what a lot of people call Rhino Farts, a little nutrients like Fermaid might help out. Second thing could be some kind of infection, are you treating your fruit with sulfites before fermenting? You dont tell us much, you added 8 pounds of sugar to a gallon of juice, 5 gallons, 10? What yeast are you using?