I don't know. From here it sounds like needle jets aren't coming off the seat like maybe a blown diaphragm, no vacuum, dirt, varnish, etc. like what you've already looked for. You said the plugs were clean and dry, too.
2013 V Star 1300 Deluxe
OEM Tall Sissy Bar
Memphis Shades Fork Deflectors
Bridgestone Exedra Max Belted Tires
Baron's RSTD 7308 bar