I don't have a starting point for the main tension nut. However years ago the "hot-em-up boys" used to give them a couple of turns in (I think) and they said they went better. (Not fuel efficient I bet). SO... (and I know it is a pain to do) you could try giving the tension nut a couple of turns in or out. (If it was not so late here I could work out which way is lean. Sure you could work it out though.
Does the cover over the tension nut seal?
When my main diaphragm split years ago the car still ran though very rough, big puffs of black smoke and it sounded at idle like it had a big cam fitted.
Other than the above, I am running out of ideas.
There are a few more experts on Ti here that may come in later.