421 sbc with 177 weiand blower wont idle down, i changed from a untuned 1050 holley alky carb they had a idle screw missing in 1 and other 3 screwed all way in on air bleeds in metering blocks to a new 1050 ATM alky carn with air bleeds 1.5 out and neither idle screw is touching. stuck at1500 rpm idle. Gaskets seem good.

check for blower holding blades open sligtly,also fair chnce it has wrong metering plate gaskets. does it stumble if you whack it?could just be lean. plus look at butterfly fit in bore and as always vacume leak.

Big blowers have a port on the rear of the case for a boost gauge port....?

You have a vacuum leak.

Do the throttle plates have holes drilled in them? This is usually done so a big cam NA engine can idle.

is blower sealed/ I have had few that leaked and would idle up. Zero boost at idle and vacuum leak is most likely your issue. Same old trick spray carb cleaner round and when idle changes you have found it.