I think I've found a great way to work out how to adjust the Haunted House VUK tube. Use the slow-mo setting on your phone to video what's happening. See attached link (
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The VUK was working only intermittently and looking at my recording I could see that the ball was bouncing off the back of the tube low down. So I moved the metal bracket (on the lower PF) forward and the ball now shoots up perfectly, every time.
Hope this is of help to others.
Matt