The pic shows a poor quality repair by the shop....
Your backfiring and stumbling, plus the vac level of 16, tells me your ignition timing os a little retarded from optimum....
If you dont have a timing light, advance the timing a little at a time until the engine pings under acceleration then back it bak just a little until the linging stops....
Check all rubber hoses going to the carb and manifold for cracks...any present will bleed off vacuum....
Good luck
