Ok, just thought someone might have an idea of the mode of failure that would warrant replacement of such a major component. No way in hell though am I going to buy a new set of TB's on a notion that they "might just be bad", without a concrete certainty that they are at fault and it's irreparable (or not fiscally sensible to, $1300 100,000mile bike after all).If we knew that (^^^), this thread wouldn't be so long...
TB's attach to the head without gaskets, rubber intake manifolds only..
As posted way earlier, I would try the sync with an actual tool MADE for this.
It IS possible the homemade manometer is NOT working correctly..
I'll see if I can get my hands on one, but based on my results not being dependent on which hose is hooked to TB #4 and my successful vacuum and pressure testing of the tool when submerged (no leaks).
Think I'm going to pull the airbox and everything around the TB's so I can better inspect where they mate to the engine and check again for vacuum leaks. Then remove the factory sync hoses and hook my manometer directly to them for one less variable.