Using nitric acid to dissolve brass

[butterchimkin]

TL;DR Summary

Safety advice for handling nitric acid.

Hello everyone. I’m a motorcycle mechanic working on a carburetor, and I was looking for advice.

To see pictures, scroll down.

I recently was working on a motorcycle, and there is a very fine brass needle called a fuel/air mixture screw that was tightened too much, and lodged in a tight airway.

The carburetor is made of aluminum. The airway is very tight, and there have been many mechanical solutions that I have tried, and none worked. I saw a solution that someone had using nitric acid to dissolve it on a motorcycle forum, and it worked for him.

I was wondering what are the safety procedures to doing something like this. How do I handle the acid, and how do I dispose of it once it’s done with?

Below I’ll attach links to the forum, and to the nitric acid that I ordered. My experience with chemistry is limited to a couple of classes in college.

Here are pictures of the needle tip that broke off, and the passage that it’s in (which decreases in diameter about half).

Here is the other side of the hole, which has a hard right turn into the brass needle about a quarter of an inch down.

Any advice is appreciated, thank you.

 

[butterchimkin]

Here is the forum I found which is relevant to this:
https://www.hondatwins.net/threads/...rass-screw-from-an-aluminum-carburetor.34916/

 

[butterchimkin]

Here is the nitric acid I ordered:
https://www.walmart.com/ip/JSP-NITR...LME96EDeCFVgSVbHbH6Z518rkKc_vs-BoC0x4QAvD_BwE

 

[jedishrfu]

What about using wd-40 or liquid wrench to loosen it up?

 

[jedishrfu]

I guess heating up the part wouldn't work right?

 

[jedishrfu]

One other thought I had was to use the liquid wrench and then use compressed air to push it back out of the hole if you can get the air into the space.

I've seen the mechanics trick of removing a stuck screw by drilling a small hole and using a screw extraction tool the extract it. However, I think in this case the pin is too small to do this and Im not sure using superglue to a rod and pressing it onto the pin would help but I mention it here in case you want to try.

 

[Borek]

Gloves, glasses, apron and do it outside (fumes are nasty). Transfer the acid with a glass pipette, have huge amounts of water to wash it out ready. I would put just a few drops on the dry part (dry to not dilute the acid), wait till I see it reacts (bubbling, if the bubbles are brown, that's great, if they are not, it is not brass that is getting dissolved), wash the acid out, dry the carburetor (even with a paper towel) and check if the needle can be removed. Repeat. Note: that's what I would try, it doesn't mean it will work, it doesn't mean it won't destroy the carburetor, it doesn't mean anything else but "that's the best procedure I can think of".

Disposal regulations can make the thing a nightmare, but they depend on where you live.

It is not as easy as "nitric acid doesn't dissolve aluminum" - in general it does. But aluminum in an oxidizing environment gets quickly covered with oxide which is highly resistant both chemically (at least to acids) and mechanically (think anodizing).

 

[DaveE]

You might also want to have some baking soda on hand, which can neutralize the acid. It will bubble and maybe splash as CO₂ is made. You'll get Sodium Nitrate as the product. I would still use water too though.

NaHCO₃ + HNO₃ → NaNO₃ + H₂O + CO₂

 

[Mark44]

@butterchimkin, before attacking the carb with nitric acid I would see if a small drill bit could push the needle tip back out. I have a set of indexed drill bits, the smallest of which is #60, or 0.040". If the needle tip is larger than this, a gentle tap might dislodge the broken tip.