On my Holley 390 it has idle ports and transition slots in the secondaries. Are you saying it doesn't have four corner idle? It doesn't have idle mixture screws, because it doesn't have a metering block. (It does have a metering plate, though).

bwhitejr

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'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

Even if you put in a secondary matering block 34-6, it doesn't have any screws either it's 'fixed'...you have idle holes in all 4 pockets and transfer slots in all 4 pockets...but you can adjust how much A/F in the idle circuit with the primaries only the secondary side is 'fixed' (unless you swap plates, swap in a block, drill or plug the idle air port in the air horn...).

-D.Idiot

My 390 has been converted to a metering block with 4 corner idle. The screws on the back side have never done doddly-sqat.

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Official Cookie and Mater Tormentor.

Ok, I think no matter the size of barrels for facing.

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Mopar Muscle is well defend by Slant Six!

Valiant Duster 1971