Ok.....I'm using the Haynes (shame on me, yes yes) Holley manual as a guide for rebuilding my carb.......come to find out that there's apparently a part missing....what is the metal plate that goes between the secondary metering block and the main body for? Will it hurt anything if it isn't there? my carb's list number is 0-80457-2 if it makes a difference....

The plate you're referring to is the secondary metering plate and it takes the place of jets like the ones in you're primary metering block so yes you need that plate unless you get a kit that does away with that plate and you then have a metering block with screw in jets like the ones in you're primary metering block.

Are you referring to the thick plate? that's there, but according to the diagrams I have, there's supposed to be another thin one between that and the main body, which is the one I was referring to.....

The diagram goes: main body/gasket/thin plate/gasket/thick plate/secondary fuel bowl

what's missing is the thin plate between the metering plate and main body, which is what I'm asking about

I just rebuilt my 4160 a few months back...I don't remember any "thin plate" between the main body and the metering plate. I'm not so sure what it would be for. I would suspect that it is OK.

Here....go here, straight from Holley's website (very helpful):

http://www.holley.com/HiOctn/TechSer...o/4150-60.html

Just click on the exploded diagram to see it in more detail. I didn't see a thin plate like you were talking about. Hope this helps...

On that diagram, it's in the upper right corner, item #151 that's missing.....

As Transambill said, if you have screw-in jets in the metering body assembly (that 'thick plate' you were referring to), then you don't have a metering plate assembly, so you don't need that plate. That plate is what takes the place of the jets on some 4160's and 4150's. If you don't have a 'thick plate' with jets in it, then, yes, you do need that plate. To sum up, if you have part #150 in that diagram, you won't need #151...that's a separate diagram for people whose carbs do not have jets to meter their secondaries...it's not really explicit on that page, I know, but not all Holley 4150/4160 carbs will have all the parts in that diagram.

Yes you'll need all the plates and all the gaskets
to put it back together again.

But instead of buying another (spacer plate) why not buy the metering block conversion kit.

This kit is available from holley and containes a new secondary metering block, bowl screws, fuel transfer tube and gaskets.

You should use #73 to #77 secondary jets after the conversion

You can make secondary jet extensions fron short pieces of
flattened 3/8" tube.

The metering block conversion kit
is pn 34-6 for carbs with side hung float bowls (1850's)
and pn 34-13 for center hung hi perf blowls (3310's)