i would do something like your setup but the top small pipe on the inlet manifold which you have blocked off, mine cant be at the moment so something is wrong somewhere on my car.

I can block and unblock the other pipes and the car doesnt mind but as soon as the top hose is blocked or put on the breather system it stalls. its should beable to still suck something through the breather as i can suck air with my mouth but it doesnt seem to be enough. its like the car is running from that tiny hole