Fuel mixture screw stuck

[dgates1]

I am working on my carburetors for a 1980 GS850GL and two of my fuel mixture screws will not come out. This is the first time they have been out as far as I can tell, the plugs were still in place. One of them is almost out and I think I can get the rest with a screw extractor on that one. The bigger issue is the number 1 carb - this one started to bind almost right away. I worked it back and forth as much as I could using PB blaster but eventually the slot gave out. I drilled this one and used a number 1 screw extractor. It was coming out a little at a time but eventually the extractor boke off in the screw.

Now I am "screwed"... I was able to drill most of the extractor out with a carbide drill bit and I don't think I have much of the top part of the screw left.

Can I keep drilling the top of the screw out until I get to the bottom post where the spring rides? Or is this a bad idea?

What size bit would I need to make this happen? and can I tap out the threads after?

Hoping someone has been here before and has some advice other than getting a different carb body.

[Who Dat?]

Well, it's evidently too late for this suggestion, but next time it happens, use a Dremel tool with a cut-off wheel to cut a slot down the 'tower' and enhance the slot in the top of the screw.

Never had to drill one out, so I have no suggestions on drill size, but the stock threads for the screw are M6 x 0.5.

[Bobbys 94]

Kinda too late for my advice but, I will give it anyway.
PB Blaster is more of a lubricant than a penetrant designed for breaking down whatever has corroded that tiny screw. Kroil Penetrant is what I've used for decades on stubborn screws and nuts. It was never designed to work in a couple minutes or even hours. Sometime days are needed to soak and do it's job.

And like our daddy's always told us " If it doesn't turn, Don't get a bigger hammer"

[Nessism]

What I do is drill a hole in the top of the screw, then pound a torx bit into the hole. That's usually enough to get the screw out. Oh, and use some heat and penetrating oil.

[dgates1]

Thank you guys for the suggestions. I had seen the torx bit working in someone's video on youtube. I'll let you know what works, if it does..

[dgates1]

So, I believe I saved my carbs.

I did get a left hand drill bit set from Harbor Freight. This worked, along with a little heat, to get out the one on #3 that was almost out.

On #1... I had to use a 1/8" carbide ball tip burr for a Dremel I picked up at Lowe's. Placed it in a drill press so I could keep it straight and running as fast as possible by adjusting the drive belts. Was able to get all the way through whatever hardened steel was left and the rest of the top of the mixture screw until I got down to the spring and post. I followed that through with a 13/64" drill bit (slower speed) and that was enough to coax the spring out with a pick. Then I got the remaining post out with some long nose tweezers as it was held in by the O-ring. Pulled the tiny washer and O-ring out with the bent paperclip trick.

This one had gotten stuck while it was still down a ways so I had some good threads at the top of the hole still. I ordered a 6M x 0.5 spiral flute tap and was able to get the rest of the brass left behind out of the threads (while it was upside-down so nothing got lodged in the tiny hole at the bottom). I then ran it through each of the other carbs just to clean up the threads.

Hopefully after running them all through the ultrasonic and using some carb cleaner after, I don't have any issues with putting in new ones.