Poor Plume. I don't think I was even aware of the bobbin tension screw until I'd be sewing for about 20 years. Whenever my tension goes out of whack it's always because the machine needs cleaning and oiling. Knocking on wood here...almost considering not posting so as not to ruin my luck. I have to remind myself that I'm not superstitious.
It does sound like you have the numbers lined up wrong, though, at least for starters. Good thing Tammi and Miriam are here to help you.