The most important thing is to use a correct screwdriver to do this. I have modified one so that the blade fits that slot perfectly. Just take a small screwdriver that is close to fitting and use your grinder to get it to fit the slot snugly. Usually this involves grinding down the sides so it will fit inside the opening to get at the jet and then grinding down the blade end so it is more "blunt".
Set the carb body on your bench so it is resting on its top - insert the screwdriver lightly into the jet hole and turn it w/o any down pressure until you feel it slide into the slot, then put pretty good "down pressure" on the screwdriver as you attempt to twist it CCW - hopefully it will"snap" loose and you're in business to unscrew it the rest of the way. You DON'T want to let that screwdriver slip out of the slot!
If the slot is good and the jet still won't budge, I then resort to heat and penetrating fluid to help. I use a 50-50 mix of Acetone and ATF (or power steering fluid). I will have another thread on penetrating fluids. I keep the carb upside down on the bench and pour this mix into the pilot jet hole (Usually if the jet is stuck, it also is plugged so the mix stays on top of the jet). I then take an electric heat gun and apply the heat around the part of the carb body right where the pilot jet sits. You will be surprised at how fast 800 watts will heat things up. When that mix starts to bubble, I again use the screwdriver as described above and they will usually break loose.
If you're working with a carb that already has the pilot jet slot "stripped out", about the only way I have been successful in removing the jet is to carefully drill it out. I start with a very small bit and try to go straight down the center of the jet, you need to be careful so you don't go through the jet and into the carb body - you can tell when you go through the brass and hit the alum. I then "work my way up" in drill bit size untill I'm at about 4mm (I believe the pilot jet thread size is 5mm). Sometimes I get lucky and the last pieces of brass will "ribbon out" as I use that drill bit. If not, then I do go ahead and run a 5mm tap in there to clean out the remaining brass. Obviously, use compressed air as you do this to clean out the "shavings" in between drill bit sizes.
This may seem to be "tedious", but have you seen the prices that "windowed" 500 carbs are getting lately.
