If the needle-valve bracket screws were loose.. it stands to reason the back-plate might not be tight.. and letting just a seep of air into the crankcase. That would create just the problems you're describing. The firewall being loose doesn't lend to a smooth running system either...

It just stands to reason in my mind.. and the needle vibes don't help either.. but keep a check on those back-plate/bracket screws.. the problem might lie therein.

Once you get it all tuned up, you'll probably find it to a whole different plane. Good luck.