Brake booster

[The_Dealer]

85 b2 2.8 fm146 durasparked with a holley 350 carb.

I've been trying to tune my carb and have been having some prOblems getting the a/f ratio and idle right. Also I've been hearing a hiss under the dash that stops when I push hard on the brakes. Also when I do this the rpms drop drastically(don't have a tach so dunno how much they drop). I pulled the hose off the booster and plugged it  and had a buddy start the rig and the idle was low(like when I push the brake hard and it drops), and the idle is nice and smooth. 1st off is this normal? I'm thinking I have a bad booster or check valve. What do u guys think?
I'm having part throttle surging and skipping but wot is fine. Getting crappy mpgs, and I'm getting lean af ratios even with a 61 jet. Others are running same setups with low to mid 50's jets

[ranger11]

The booster is prob bad. The idle shouldnt drop with the booster port blocked off. You have a massive vaccum leak (the booster) and its causing it to idle high. Also you can put your hand over the top of the carb and see if the engine shuts off if it dont that will confirm the vaccum leak.

[rabunjeeper]

 {agree}

[The_Dealer]

Ok thanks guys, just like I suspected.well I'm off to get a new booster