Here is an excellent article concerning slavery in 1776 and the Founders. The majority of the Founders thought the institution of slavery was evil. Revisionists try to make the Founders into evil racists to undermine the brilliance of these men and their ideas. Slavery existed in the colonies hundreds of years before 1776.
One of the strongest abolitionists was John Adams who never owned a slave. They created the seeds that led to the abolition of slavery in certain states right after the Revolution, but were not entirely successful in some states because slavery was such an entrenched, ancient (accepted) institution, practiced throughout the world.
http://www.wallbuilders.com/LIBissuesArticles.asp?id=122
bookmark for reference - founders and slavery