OK. So here is the write up on how to get to the air/fuel screw on a stock Mikuni BSR carb.

To start with. You will need the following:

A drill. As you see mine is a corded model. Cordless will work just fine.
A screw of some sort (sheet metal screws work best)
A scrwdriver appropriately sized for the screw.
A drill bit that is appropriately sized for the screw.
A pair of pliers.
And last but not least, your carb.

Here I'm using a bare carb I have laying around for demonstration. This a stock carb from a 2004 LTZ400, stripped for parts!



First off. Find the plug that covers the air/fuel screw. It is located on the bottom of the carb. It will look like it does in the picture:

(Note: Its what the drill bit is pointing at)



Now, as you've seen, Suzuki was nice enough to make a pilot hole from the factory.

Now load your drill bit into the drill, and drill through the plug. BE CAREFUL!!!! Let the weight of the drill do the work, as soon as it breaks through STOP! The screw is located directly behind the plug and we dont wanna mess the head of the screw up.

After you are done drilling you will have something that looks like this:



Now grab your screw and your screwdriver and thread the screw into the hole you just drilled. It will look like this:



Now grab the screw with your pliers like so:



After some wiggling and some pulling you will end up with something like this:




Now you can adjust your air/fuel screw. Hope this write up helps!

great job. i have been thinking about doing some write ups so i dont have to answer the same questions over and over

The real damage isn't in screwing up the head of the fuel screw - it's a flat-tip for adjustment. You won't make a hole in the brass fuel screw so bad that you can't find a flat-tip screwdriver that can't do the job of adjusting it.

The real damage is in driving through that brass plug, having the drill bit bite directly into the fuel screw, then bottoming the fuel screw so hard that you break the tip of it off in the carb body - which trashes the carb, because it permanently seals the pilot circuit fuel delivery hole forever. That's FOREVER. You can't get it out, and you can't pay a shop enough to try to get it out...

Push on the drill too hard, bust through that cover, bite into that fuel screw and bottom it so hard the tip snaps off in the carb body - then buy a new carb, because yours will never idle, or have any kind of 0-to-1/4 throttle response...

The hazard here is not damaging the head of the fuel screw...

This is the exact reason all jetting instructions say "Lightly seat the fuel adjustment screw..." - you can break the tip of it off with a screwdriver under regular pressure, if you're not careful - let alone a drill that's turning high RPMs...

Drill SLOW, with a variable speed drill.

Excellent info! I've never hulked on drilling the plugs before, so I've never experienced that.

When I did mine I use a reverse drill bit the came with my screw extractor set and the brass plug just spun up and out. Just another option.