Do you get a Hissing sound when you open the fuel filler?
Blew out the air intake and overflow hoses with compressed air
Any chance the "loud metallic grinding" is unrelated to the hesitation and stalling? What spark plugs did you use and did you gap them to spec? It sounds like you had a slight hesitation BEFORE
you did all the work and now you have more or worse symptoms. Is that right? The Big Brass Screws should be out more than 1/4 turn to get the 1200 RPM you're shooting for. Something is off there. What did you use to do the TB sync?