I'm rebuilding a Holley 4180 that I don't think has been apart since '86. It was really fun getting the original black gaskets off. CRC Gasket Remover isn't all that it's cracked up to be, although it helps one layer at a time...

Now I need to remove the two pressed tamper-proof plugs so I can get to the idle screws. The Holley kit instructions say to center-punch them (no problem), then drill a 3/32 hole through, then an easy-out. But that hardened steel just laughs at any drill I have, and my carbide burrs don't have sharp teeth on the end.

What do you use to get them out without destroying the casting around them?

Pic's please, Something doesn't sound right

I'll post some pics tomorrow if you really want them... but in brief, for each adjustment (my carb has 2, but some have 4) there is a boss cast into the baseplate. Each has a welch plug about 5/16" in diameter, installed backwards (lip toward the carb) so I can't just grab it with a screw extractor. Behind the plug is the idle mixture screw, which has a special head, although I've read that the right size Allen wrench will work.

This carb originally came off a '86 or '87 Ford truck, with either a 351W or 460. The primary bowl actually has cast into it, "Manufactured by Holley for Ford". They apparently really went out of their way to make it difficult to change the idle mixture, and I think the plug is actually hardened steel too!

Me I would start with the smallest drill (bit) and work up from there. Hardened for a reason and that's why they are called tamper "proof" and not tamper resistant. Seem to be working says the EPA and CARB

Yeah, so far, but they're not going to win this one in the end (especially with an old vehicle and living in a non-emissions county!)

I'm considering tacking a 1/16" welding rod (or using my body-work stud welder) to the plug, then I can just pull... but a little too much heat and I'll melt the tip of the aluminum boss. Oh wait, I'm not putting the stupid plugs back in anyway

Plugs are steel? (check with magnet)

carb body aluminum?

heat carb body
then chill plug with dry ice or copper wire chilled in freezer.

A “wart freezing kit” from a drug store might work if your local grocery stores do not have a dry ice freezer.

The two metals have been in contact a long time and iron/aluminum corrosion may have “glued” them together

Can't picture the Holley setup but on GM Rochesters we used a cutoff wheel to cut a slot in the bottom then take a punch and basically bust the plugs out. They're hard(brittle) so it didn't take much once you got behind them. Pics would help us.

AHH you left out the oddball carb part (ford application)
I would follow some of the previous suggestions and offer a few more
1. if you can find an appropriate size bottoming tap, you may be able to thread the cup enough to "Pull it out" with nuts & spacers.
2. A left handed drill may work
3. Depending on the depthe of the cup, once a hole is in it you may be able to "Roll" it out like a freeze plug.
4. Heating the aluminum with a small butane micro torch and quickly goiing after the plug may work as aluminum expands fairly quickly.
5. carbide tipped cement bits work well on hardened steels and they are dirt cheap. I would STRONGLY recommend using a drill press or mill so you have better control over the feed. You do not want the drill to get pulled in to the adj. screw
Again a few pic's would help

keep us posted

Thanks for the suggestions. I should buy a set of left-handed drill bits someday.

I got them out, but not without a struggle. Tamper-proof, my ass

First I tried to get a 1/16" welding rod to stick (usually the opposite of what I'm trying to do!), but ended up gouging a small pit in the plug instead.
It had gotten hot enough that the temper was gone and I could drill into it with a #36 (picked that size in case I had to tap for a screw thread) deep enough for an easy-out.

For once, an easy-out actually worked. Turns out they aren't welch plugs but a piece of solid steel rod about 1/4" deep.
Now I'm going to cut a small screwdriver slot in the heads of the needles with a Dremel cutoff wheel so I don't have to use an Allen wrench and hope it doesn't strip out. Then it all goes back together.

Here's the "before" picture of one of them for TJP (The secondaries have the bosses also, but they're not drilled. Just a "dribble hole" in the venturi).

Sounds like successful tampering to me
What they meant by "tamper proof" is non-tuneable, factory settings...

Dremel with those small carbide engraving bit is a wonderful tool for controlled grinding, centering, etc... on difficult carb plugs.

Carbide tipped drill bits will cut through broken high speed steel drill bits and broken EZ-Outs like butter. They should make short work of that. Use slow speed. You want one that looks like a normal twist drill, but has a little chip of carbide brazed to the tip like this:



https://www.amazon.com/Jobber-Carbide-Tipped-Standard-50359/dp/B00PM4T9QU

These will work in a pinch
CHEAP ALTERNATIVE

Horror freight has a set for 6.00

Cheap brittle taps and drill bits have greatly stimulated my creativity to invent new curse words

that reminds me of my old man.............
one day, way many moons ago, he was doing some repair work at the Eagles Club here on main st. [he was a trustee for very long time before he passed].
he needed a 1/4" drill bit, and although the house was only a tick over a mile away, he didn't want to drive home for one.
as there was a G.C. Murphy 5 & 10 cent store right across the street from the Club, and there were a few patrons "holding down the bar" [as the old man would say] he sent one of the most trusted [?] patrons across the street to get a 1/4" drill bit.
since Murphy's didn't sell bits separately, a "complete quality set" was purchased for the princely sum [at the time] of $4.99 [plus tax of course].........
the old man grabbed the 1/4" bit, stuck it in the drill, and proceeded to drill the hole.
when the hole broke through, it promptly bent into a 90 degree angle without breaking, causing the drill to be whipped from the old man's hands. the bar patrons ROARED with laughter, causing the old man to say lots of "bad words" !

then there was the time my brother was installing a metal stair railing in a loft apartment........
the railing was just your cheap-o home improvement store pre-made chinesium, painted black with the twisted uprights, needing holes drilled in the base[es] to mount to your stair treads.
the chinesium drilled easily until the last hole. that one seemed tougher than the others, and looking at the bit, little bro saw it was getting a tad dull. he figured since it was the last hole, no big deal, since the chinesium must have been really tough on the bit, he would just finish the hole and toss the bit............
heaving on the drill until it started to slightly get "real warm", he FINALLY got the hole through !!!!!!!
looking at the bit, he was surprised to find the tip of the bit BLUE !
well, the hole was through, and he was gonna toss the bit anyway.
firing up the drill to cool it off, he found.............the drill was in REVERSE ! .............boy, did we howl when he told that story !