No fuel will flow out.....the fuel level in the float bowl is down near the height of the gasket where the float bowl meets the carb body.

If you are drilling and using an screw extractor.....I can't imagine trying to do that job on the bike.  It is tough enough to do it when the carb is up on the work bench.  If you find the new screw is really tight.....the threads in the carb body are corroded.  I have a tap you can use is you pay shipping both ways...and a small deposit so that I can be sure I get it back.

No way would I attempt drilling in something awkward to get and maintain square to.
50/50 acetone and transmission fluid, great penetrating oil.
Online comparison of all.
WD 40 sux.

OK that carb body is hard to find and very $ new so i would take it off strip it down  and find a good machine shop/friend  who will set it up in a drill press and reverse drill and rev tap to remove broken part . you will only get ONE chance at this ,use it wisely  eta have the new part with you so the driller will know the architecture of area and provide a better result

chxeckmate:

I almost found out the hard way.  I bought a theft recovery bike a while back, and it had a carb with a stubborn idle mixture screw....and somebody had boogered it up and the screw slot was damaged too much to allow a screwdriver bit to remove it.  I drilled it and used an extractor to remove the old screw.

When I went to put the new one in....it was incredibly tight.  I tried lubing it up, and it still was too tight and I almost ruined the brand new mixture screw.  I bought a tap and ran it in/out of the whole...and the new screw now works as it should.  The aluminum threads were a bit corroded and needed to be cleaned up. The threads are a 6mm x 0.50, which is a very fine pitch.

Canadian_kiwi stated it is an "air mixture screw"....I believe we all know that on this carb it is a Fuel Mixture screw and adjusts the amount of fuel flow. (Some carbs do have air screws, and they are located on the air filter side of the carb body).

And I believe everyone understood it is the soft brass screw he is trying to remove.

gizzo wrote on 11/25/15 at 13:04:35:


The melting point of aluminum and brass are pretty close.  That trick definitely works with aluminum and steel where the melting points are so far apart, but I'm not sure about aluminum and brass.

What penetrating oil are you dosing it with?
Time, with it sitting so it's holding the penetrating oil, and let it sit.
Before heat ,strip it down, and heat and a quench, heat and quench, can cause the corrosion to get broken down. Doesn't work every time.
The carb is tilted. Any time water gets in , and sits, see how it is..

Anything you can do Safely,to make it easier for a machinist, will save you money. I cleaned up and removed the snap ring from an Explorer rear hub. First, the nearest nice mechanic. Blew the seals on his press. He fixed it, tried again, decided no to, sent me to a machine shop. Twenty bucks,, pressed out, New bearing in, snap ring, ready to go.
Attitude is everything.

Calling, asking, versus walking in with it, I usually just walk in, and I get treated great.
And one chance really is all you get, and IF you start and decide you'd rather pay someone, but you've got an off center, angled hole started,the machinist is in worse shape and you'll spend more.
At minimum, if I didn't have a drill press, I wouldn't try it.