Hi Kerry,
With woods we all tend to put a little more effort in for some unknown reason, (although it is usually trying to lift the ball) this may cause a simple overthetop downswing due to the violence in the swing.
Hence the reason you only do this with the longer
clubs, another thing you should not ever do is keep aiming further down the left to compensate, like closing the clubface at address this only makes things worse. Golf is a game of opposites, for a test try teeing up on the left side of the tee box next to the marker and aim down the middle or slightly to the right of the fairway you may be suprised by the result.
Hope this helps
Ian