Holly Metering Block Issue

Is it possible for gas to leak around the idle mixture screw cork seals while the engine is off?

As i was waiting for a new set of 8.5hg holley power valves to arrive by mail for my 670SA carburetor, i put on my holley 770SA in its place for the meanwhile to keep my mailbu running.

Since i had a damaged power valve in the 670, i began to question the one that was in the 770SA, same 8.5hg, so i removed the front fuel bowl and metering block to remove the power valve, it checked out just fine using home made tester.

As i was inspecting the rest of the metering block, i noticed slight fuel staining around the cork seal area, not leaking at all, so i removed them and put the only two new cork seals i had on hand, and screwed in the idle mixture screws like they were set by number of turns.

I put the the metering block, fuel bowl and their respective gaskets back the way they were, snugged the fuel bowl screws in lightly like i've always done in the past with zero leaks afterwards, poured the saved gas back into the front vent, and almost immediately noticed fuel driping from the metering block/fuel bowl area from somewhere without touching anything else.

So i snugged the fuel bowl screws just a pinch more, that didnt help, i though maybe the accelerator pump diaphram by chance started leaking, but i never messed with it, and besides, that should be completely dry till you start moving the carburetor throttle arm, then i removed the fuel bowl and metering block once more, and this time i saw the idle mixture screw cork seal were soaking wet with fuel when they shouldnt be.

Figure thats the ONLY thing i changed on the metering block was the idle mixture screw cork seals, i remember they didnt fit so tight after inserting them the correct way, bevel side in, so i figure that has to be it, and after 30yrs of using and rebuilding holley carburetors, this is a first for me. If onlyi had never checked for the power valve status or just left the original cork seals alone, the carburetor worked just fine and leak free before i touched it, now im gong to have to locate/buy more seals, i have zero on hand now. Im going to pull the 770SA off the enfine, put it on my jegs carburetor rebuild stand while sitting inside my old 700r4 transmission pan to contain the leaking fuel, then pour some fuel through the vent and see first hand where the fuel starts to leak from.

I read online on a random forum recently, there was a mention of a possible hairline fracture in the metering block near the idle mixture well area allowing fuel to seep in when it should be completly dry till the engine is running... i have not a clue, if so, a replacement is no big deal, a 3310 metering block will work, the 770SA metering block has exactly the same IFR/PVCR/emulsion/anti syphoning sized holes, also the IAB/HSAB front and rear are damn near identical, i have a complete 3310-2 from the late 80s as reference.


Any thoughts, anyone been down this road before?

To be honest... i've never heard of a holley metering block fail.

Has anyone ever used another form of idle mixture screw seal other than cork.... theres o-ring(pic1) and urethane(pic2) seals available as well.

From the description i've read... the urethane seals are for the billet blocks, would they even fit the holley zinc metering blocks?

Ok,,,,, it was the cork seals.

The replacements i used came with a set of holley idle mixture screws in a small clear resealable baggy i bought as extras off ebay, thought nothing of the seals, they looked correct, so i used them.

Since i didnt have any extras laying around, i opened a sealed holley trick kit(37-754) for my 3310-2 i've for about 3yrs now, and took the two idle mixture screw cork gaskets and installed them on the 770SA metering block, they fit more snug and zero leaks with the engine running and after shutdown.

Awhiles back, i bought a proform(67166c) primary billet block(black) w/timed port, adjustable IFR/PVCR with blockable emulsion holes(4 per side) and it had those urethane seals for the idle mixture screws, talk about stupid tight for the screws, had a hard time turning them, so i used a pinch of WD40 on the threads so they would turn a little easier, and they appear to be the same dimension ID/OD as the rholley cork screws.