Broken idle screw tip

[Seppi72]

In refreshing my 40 DCOE carbs, I've found that one of them has the tip of the idle screw lodged in the orifice of one barrel.  I've included pix of both barrels so you can see both the clogged one

as well as the open one.

Does anyone have a suggestion for how I might remove this broken tip without doing significant damage to the barrel?

I'm thinking that after filling the screw hole with Kroil and letting it sit for a few days, heating the carb body with a propane torch will somewhat enlarge the orifice and perhaps facilitate removal.  But how should I go about pushing that tip out?

[jitenshakun]

I'd tippy-tippy-tap-tap the end with a small pick or the world's smallest punch. You might get lucky and it'll pop out.

As a less invasive approach I'd try compressed air from the throttle body side. Again, you might get lucky and it'll pop up and out.

[Patcon]

I think your idea is good, unfortunately if someone cranked it down really hard it can damage the body

[ETI4K]

I think I'd use a flat bar, about 1" wide, and round one side to match the radius of the bore.  Use it press on the exposed tip.  The radius-matched tool won't damage the bore, and by virtue of it having some heft, you'll be able to align the force vector with the axis of the tip.  Hopefully, this will minimize any reshaping of the hole.

[Seppi72]

An excellent suggestion, ETI4K.  I have some 1" diameter stainless steel tubing so I might try using that as the pusher and a thin oak slat on the other side of the bore.  I'll then drive an oak wedge between the two to apply force to the broken tip.

[ETI4K]

I'd love to see a pic of your setup.  I like the wedge idea.

[Seppi72]

Success !!  The broken idle screw tip is now but a memory and I can see light through the hole.  Now I can resume refreshing this carb and not have to purchase a new 40 DCOE for about $350 from www.carbparts.eu in the Czech Republic or even more from Pegasus Racing here in the U.S.  I also have learned that simply buying a new aluminum carb body is difficult, if not impossible.

I did not end up using mechanical force to remove the tip.  In looking through old threads here, I found someone who had the same issue several years ago and resolved it using concentrated (conc.) nitric acid (70%) to dissolve the iron tip while leaving the aluminum carb body intact.  As a retired chemist, that approach appealed to me and that's the route I eventually took.  There is also a similar technique using a boiling, saturated alum solution with YouTube videos to back it up.  I tried that approach first and was unsatisfied.  In addition, the alum treatment darkened the aluminum alloy.  So, nitric acid it was to be.  But, just a warning to any others, it has to be conc. nitric acid as that will passivate (and thus protect) the aluminum surface.  Dilute nitric acid will react with aluminum.

Fortunately, I had a small amount of conc. nitric acid that I had brought home from work many years ago just to have it "in case."  Well, this was the case and it was just as well that I already had some because obtaining conc. nitric acid is not that easy to do here.  There's no problem if you want to buy conc. hydrochloric acid (muriatic acid) to do cement work as you can get that in any hardware store.  And if you want conc. sulfuric acid (oleum) to top up a car battery, you can get that at any auto parts store.  Both are exceedingly dangerous chemicals and must be handled as such, but no one will question your intent.

Not so with conc. nitric acid.  To my knowledge, it's not available in local stores; and certainly not here in my small town.  People also seem to assume that you're going to use it to make explosives so that many chemical supply businesses ask a lot of questions and have rules about who can purchase it, shipping, etc.  But, I did see where you could order twelve, 1-ounce bottles through Walmart.com at a hideous price.  But, if you need it, you need it.

In order to be the most effective, I blocked off the channel between the idle screw and the progression holes on the top of the carb using butyl rubber as it would also be unaffected by the acid.  I placed the carb body on a level surface and used a small eyedropper to fill the idle screw hole to the top with acid.  That didn't take a lot of acid, perhaps one mL.  I think I initially saw some bubbling but that isn't important.  I replaced the acid twice a day.  The process took a long time to achieve the desired result. 

The "tell" of success was when I saw liquid leaking out of the bottom of the idle screw hole.  That took about a week.  Once this happened, a small pick was used to push the screw tip remnant up into the port where it could be removed.  There is no obvious damage to the outlet hole.

I know that I've gone on a long time about this but I think it's important to provide as much detail as possible so others can benefit from my experience.  I'll probably write up a technical article on the matter.

Edited November 5, 2021 by Seppi72
Cleaned up language for clarity.

[jitenshakun]

Wow - this is amazing information. Thank you very much for sharing!