I have used the King James text as a basis for my translation to save time in performing a fresh translation, and because it is a word for word translation of the original languages. Many new translations try to interpret the text, but often fail to do so well.
The Old Testament has been faithfully preserved through the centuries by the Jewish people in what we know as the Masoretic text. From my experience with translating this text there are very few copyist errors and for the large part has come down to us very true to the word of God.
The King James version is also based on a more reliable version of the Greek text for the New testament than later translations. The King James is based on the Received text which represents the bulk of the old Greek manuscripts that we have and they agree with each other almost perfectly.
Newer translations are generally based off the Alexandrian text who’s earliest known copies date back before the Received text but are much less in number, seemingly meaning they were less used by early Christians.
Jay P. Green, Sr., General Editor and Translator of the Interlinear Greek-English New Testament, states in his preface:
“The market-place is being glutted with new books which are being represented as versions of the Bible. Each one claims to be the very word of God, yet there are literally thousands of differences between them… they all leave out dozens of references to the deity of Jesus Christ, and they add words which tend to question His virgin birth, His substitutionary, fully satisfying atonement. This is due to their decision to depend upon an Alexandrian [Egyptian] textbase, instead of that body of God’s words which has been universally received and believed in for nineteen centuries, known to us as the Received Text. These new versions [such as the NIV, New Jerusalem Bible and others] are not only marked by additions, but also by subtractions, since some four whole pages of words, phrases, sentences and verses have been omitted by these new versions. And these are words attested to as God’s words by overwhelming evidence contained in all the Greek manuscripts…
…it has been written, ‘For I say to you, until the heavens and the earth pass away, in no way shall pass away one iota or one point from the Law, until all things come to pass’ — Matthew 5:18 [Green’s paraphrased]
What then is the evidence these Bible-alterers offer to persuade you to give up the precious words they have removed from their versions? Mainly, they cite two manuscripts, admittedly old, but also admittedly carelessly executed. The Sinaiticus was so poorly executed that seven different hands of “textual critics” can be discerned as they tried to impose their views on the Bible… it was discarded, found in a wastebasket fourteen centuries after it was executed. The Vaticanus manuscript lay on a shelf in the Vatican library at Rome until 1431, and was considered so corrupt that no one would use it… they have systematically removed Luke’s witness to the ascension of Christ and of course they have done away entirely with Mark’s witness to the ascension, simply because these last twelve verses do not appear in those two corrupt manuscripts, the Vaticanus and Sinaiticus…
… Origen, an early textual critic… said, that ‘the Scriptures are of little use to those who understand them as they are written’… given the opportunity, many like Origen will actually alter the manuscripts to make them say what they understand them to mean… Justin Martyr, Valentinus, Clement of Alexandria, Marcion, Tatian, and a horde of others practiced their ‘textual science’ by operating on manuscripts, or by writing their own ‘versions’…
…Today there are more than 5,000 manuscripts and lectionaries in Greek as witnesses to the New Testament text. And 95% of them witness to the Received Text readings [contained in Green.s Interlinear and the King James Version]. Partly due to the fact that ancient manuscripts containing the Received Text were worn out by use, while the Alexandrian textbase manuscripts were preserved by the dry conditions of Egypt, some have sought to discredit the Received Text because they say it is not ancient. But now that manuscript portions from the second century are being unearthed, it is found that many of the readings of the Received Text which had been tagged scornfully as ‘late readings’ by nearly unanimous consent of the ‘textual scientists’ are appearing in these [newly found] manuscripts. Readings which were before called late and spurious have been found in these early-date manuscripts… Yet strangely, in textual criticism classes, such discoveries are swept under the rug, not reported to the class.”