DCOE 40 Idle mixture screws are stuck/broken off HELP!!!!!!

[adamr]

I have a set of very slightly used triples on my Z. I discovered while trying to adjust the idle mixture screws, that the very tips of 4 of these have seated themselves in the body of the carbs, and have broken off. It appears that the PO might have overtightened them. I am able to completely remove all of the screws. It is the tips (about the diameter of a paper clip) that are stuck. My attempts to remove them have proven unsuccessful. If I play with them anymore, I fear I will do damage.

Does anyone have experience with this? If needed, I'll ship them off to a pro.

Thanks for your help!

[adamr]

Anyone?

[zKars]

Wow, tough one. I think your only hope is to try to poke the remaining tip out of the hole from the other side. The schematic blowup I have kinda suggests the there may be access from within the main bore directly beneath it, but even so, you'll have to come up with a very small diameter, and very stiff tool, like a 90 degree ended dental pick maybe? to have any hope of pushing it out.

What you may be left with though is a hole that may not perform like the original hole if its too deformed. Even if you drill them out with a small wire drill bit, it may require some welding up and re-drilling with the right size, and in just the right spot. At the very very least, you'll have to make all 6 behave the same way!

That's step two, after you extract those tips.

Good luck

Edited September 21, 2011 by zKars

[adamr]

JIm,

I tried pushing it back thru to no avail. Solution found: I was referred to a local machine shop. They have an acid that eats steel/brass, but not aluminum. Can't remember what it's called. It worked. New mixture screws on the way from Pegasus racing, who, I'll add, has excellent customer service!

Machine shops were rightly concerned that attempting to drill out the metal would result in the drill bit 'walking' and drilling into the softer aluminum carburetor body. Acid, followed by an acid neutralizer worked perfectly.

Thanks for the response, Jim.

[zKars]

Brilliant solution!!! Great to hear you found a fix.

You have to find out what that acid is. Extremely useful stuff. Won't use it often, but when you need it, you need it!!!!

This makes me think of applications like melting a broken off steel exhaust manifold stud out of an aluminum head... Probably overkill, but any chance to work with fire, explosives or dangerous chemicals must not be missed!

[ol doc gully]

any chance youve found any more info on that acid?

i have the exact same problem, although thankfully only one needle broke. was just about to drill it out and came across this, i have some chemist friends that can hopefully help shed some light...

[240260280z]

Nitric acid... but it is explosive and a controlled substance due to this. found this on the net:

Let me try and dissuade you from this idea. I presume that what you want to do is dunk the entire carburettor in an acid bath and wait for the brass do dissolve. Both sulphuric and hydrochloric acids chew aluminium as well as brass, so the only candidate is nitric acid, which dissolves the brass but puts a layer of oxidation down on the aluminium surface which prevents further aggression. Nitric acid is nasty stuff to handle, and I suspect you would also have to polish off the oxide layer for the best airflow.

[240260280z]

[ol doc gully]

Ah, nitric acid, very good to know, that should be enough to get me started in really figuring this out - thank you.

The main reason I've been debating it is because I fear that the passage below the seat (45 DCOE 152) is tapered, so that if i were to drill it, it would not be right - can anybody confirm or deny this?

I already have a 1/16" bit that looks to be just about the right size... tried heating and forcing back through from the carb throat but it only bent broke and mushroomed

[240260280z]

it is tapered.

[240260280z]

Maybe not:

Edited November 7, 2013 by Blue

[ol doc gully]

yeah, i cant get a good picture, but it looks like the initial seat just below the threads has a quick/shallow taper but then the orifice going down into the throat looks straight walled...?

thanks very much for your help and input