Fuel lines are separate. Air goes through the throttle bodies and through the silicone hoses, through the inlet manifold and then into the ports on the cylinder head. Fuel is then separately injected via the fuel injectors.
I think carbs would be different where fuel and air mix in the carb.
But you're still using the injectors in the ITBs I assume, so what's passing through the hoses is an air/fuel charge mixture? I've seen cases where that's been sufficient to degrade the silicone hoses over a long period of time.
PTFE lined silicone, I hope. Standard silicone and fuel don't mix nicely IME.