removing broken carb mixture screw, need idea

[1 FMF]

in cleaning out the carbs on my outboard I broke off an idle mixture screw such that the remaining piece of the screw is in the carb. I have a new screw on order, so the problem is getting the old screw out without hurting the carb body or the threads. Need some advice.
The mixture screw is brass. The carb body is aluminum. This is on a small, brand new, yamaha outboard.
The screw diameter is about 1/8", maybe around a #6 in size, but metric. The screw stuck out about 1/2" from the carb to give you something to turn, but I broke that off and what's left resides about 1/8" to 1/10" below the surface.
My biggest concern is not messing up the threads in the carb body.
My thoughts, unless someone else has better idea, are to try in order:
1) either superglue or epoxy the broken off piece and hopefully have it hold just enough to unscrew it.
2) if that don't work try using a sharp hard steel flatblade to etch the screw so i can unscrew it with a flatblade screwdriver. hopefully the brass is soft enough i can carve just enough to use a flatblade?

.. thought about using a dremel cutoff wheel to carve a line but I think the screw is so small recessed to far so the cutoff wheel will end up carving the body and the threads. Plus i'd have to wear away a cutoff wheel from the 3/4" or 1" diameter they start out at down to about 1/8".

 

[WalterMitty]

Try using an "Easy Out".

http://www.toolprice.com/product/1218A

Put some penetrant in the hole to start. The way these things work is that you drill a hole, very centered and very straight, into the broken screw. The easy out has a reverse spiral on it that digs into the hole you drilled and may get the rest of the screw out.

Or you may get to buy a new Carb.

 

[mechtech2]

A fine sawblade can be used, or a hacksaw. Then unscrew the part normally.
Just cut BOTH the surrounding area and the stub - don't worry about cutting the aluminum - you aren't going very deep.
You may need to heat it if it doesn't come out readily.

 

[dwendt44]

I've seen reverse twist drills, but I don't know where to get them; bummer.

 

[c502cid]

Any way you do it, take the carb off the motor first, no matter how much of a hassle it might be. You reduce the risk of making a bad problem worse just by taking this step.

 

[Merkava_4]

You're going to lose the threads, but don't worry, you can replace them with a Heli-coil insert.

Get a drill bit the same size outside diameter as the broken mixture screw.

The reason for that is to keep the drill bit centered. A small drill bit would just wonder all over the place and do more damage. Besides, you need to remove all the leftover screw for facilitating the installation of the Heli-coil.

You don't want to drill all the way into the orifice; drill just deep enough to clear out the threads of the broken screw. Once you get that part drilled out, the rest of the existing screw will just fall out.

Assuming that you have enough "meat" around the mixture needle hole in the carb body, the Heli-coil drill bit will drill the hole the right size for the Heli-coil threads.

Now tap out your Heli-coil threads.

Thread in your Heli-coil insert.

Break off the tang at the bottom of your insert.

You're done!