2007 VTX 1800N (N1), Vance and Hines (baffled), stock intake, 23K miles and growing
I've seen vinegar and something to knock the rust off (dog chain, etc.), Muriatic acid, electrolysis. Vinegar needs to sit for days because the acid is weak. Muriatic acid can't sit in there for too long and you don't want to breathe it in!, Electrolysis requires venting and multiple attempts depending on how bad it is. Tons of videos out there. Oh, and CLR.