Its not a "you ask we tell" situation. Your opinion doesn't change if I want a new exhaust on my bike, I don't care that the carbs need tuning, hell, my little wr250f needed to be rejet with just the baffle removed. I understand how these bikes work, and I've asked how things perform and I get "keep it stock" with no explanation. This isn't just a "Help my head gasket is leaking" forum, its for a collection of riders with the xs400 and that's where the problem starts, with people like you who buy 5 xs's and keep them all stock and tell other people to keep it stock, just because "ohh it runs better stock" when they asked a question about changing exhausts. If someone asks a question and you immediately say "keep it stock" with no other help, get off this forum.
I understand that you think you're some mechanic or something, but I've also been working on bikes since I was little and I understand how engines and carbs work. I asked if anyone has used those performance carbs because they don't use vacuum operated secondaries and look to be easier to tune, therefore I was getting some confirmation.