Racing Fuel Systems

Attached is a picture of the pair of metering blocks for the 8156.

This is the very first 4 corner idle carb .Holley released this in 1978.it is the same as a 4779, but has the old style progressive linkage.

Which block is the primary? They are identical with the exception of the top well plugs

A closer look should show they're not identical, regarding booster feed passages. The secondary block, with high up main well cup plugs (inner two), due to booster feed passages that do not angle downward. The deeper cup-plugged main wells metering block should be the primary, due to angled downward booster feed passages.

I took another look, both have the exact well plugs, inners are deep.

The primary (I assume) has the plug sticking out for ported vacuum.

The secondary has a kill bleed in the angle channel, just like the primary, but looks like it was added, but usually they have one in the upper Chanel, this one does not.

Do 4 corner blocks have the same configuration front and back?

Can someone explain why the kill bleed in the angle is different than the one up top

Better picture

Usually the "kill bleeds" will be located in the top #22 or in the dimple just below #8 in the metering block picture, however some can be higher in the emulsion channel toward #8 and sometimes not even present on the secondary block.
The most inportant thing is that this bleed hole is above the fuel level at all times, as long as it is it will function properly. The upper #22 is the most common location. There are some applications where that bleed shoud be as high as possible, usually off-road trucks that do a lot of bouncing.

Yes the top metering block in the picture with the plugged vacuum advance port is the primary.
Here is a picture of what " gntkllr " was referring to. You can see the different angles where the drill bits are inserted.

Thanks guys.

Should you have a kill bleed in the secondary block as well?

Does it matter if it is located in #8 or #22?

Should be about .028" . The 2 corner idle carbs I see/rebuild do not have a kill bleed in the secondary block.
Al of the 4 corner idle carbs on my shelf have the kill bleed in secondary block as I described.

Thanks guys. If I am building a block and it already has a bleed in #8 and not #22, is that ok? Or should I plug it and drill for #22