In 1807, england passed the Abolition of the Slave Trade Act which
made the previously immensely profitable (or so I understand) slave
trade in Africa illegal.  Was this solely an act of concience?  If so,
what prompted it.  If not, what was the motive.  Please cite your
sources in the text of your answer.

Aaronvl,
You point out correctly that the Act just abolished slave trade for
British ships with Africa, import of new slaves.  Traffic between the
colonies could continue.
This termpaper adds some insight:

http://www.collegetermpapers.com/TermPapers/Sociology/None_Provided17.shtml

While it speaks of anti-slavery movements in the 18th century, it
suggests that the act resulted more from economic considerations as
the industrial revolution increased productivity and reduced the need
for manual labor.
So in answer to your question:  it was not "solely an act of
conscience," which can also be surmised from the fact that the 1807
act did not abolish slavery, per se.

This occurred in 1833 with the slavery Abolition Act that outlawed
slavery in all British colonies (it was never legal in England under
Common Law), realistically allowing a four-year phasing out period to
avoid collapse of economies dependent upon slavery.  You can read
about this here:

http://www.anti-slaverysociety.addr.com/huk-1833act.htm

This is a site found as a link in the following site that provides
many links on the subject.
http://www.ucalgary.ca/applied_history/tutor/migrations/four5b.html
http://www.antislavery.org/breakingthesilence/main/02/Howprofitablewastheslavetrade.shtml

This is a lecture which touches on the profitability, suggesting that
in the 18th century it may not have been so immensely profitable,
which is logical in a period when the trade was unrestricted and open
competition existed.

http://www.emayzine.com/lectures/notes%20africa%20slave.htm

After the 1807 act, the profitablity of individual voyages would
probably have increased with a greater risk.

I hope this can be of some help.
Myoarin