I have a HUO Dredd that has been in our family since it was about 2 years old. I think there is a timing issue of some sort with the left shooter. In the mode where the ball is held there until you hit the fire button to launch toward the targets it fires fine. When the ball goes to the left shooter at other times and is immediately ejected, it launches with much less force. It is as if the plunger fires before the ball is fully seated against it. I am wondering if there is some sort of adjustment that has to do with the roll over switch that triggers it.
Not sure if this makes a difference, but I found when I installed the deadworld mod that it is a very early production machine and I just had to change out the plastic ring for it to lock the balls there. Some of the switches were numbered differently and in different locations around the deadworld.