Ok, I contacted Weber and this is what they said:
Well your missing one
carb wont run with this missing
these are idle jets not screws there should have been a brass threaded jet holder and a small jet that pushed into it in the missing hole
confirm the jet sizes and we can help with two issues improved economy and performance
If you have the jet and just have it out to look confirm the sizes and the current best idle settings for the idle speed screw and the idle mixture screw
confirm how many turns in the idle speed screw needs to be to attain an idle of 850 to 900 rpm
confirm the number of turns out on the mixture screw to find the sweet spot smoothest best idle location. with these numbers and the jet sizes we can confirm your calibration correctness for econmy and performance with the current emissions fuels being supplied.
fuels do change each year and if this carb has been on for a few years it would be something that will help to improve the function of your carburetor no rebuild needed jet recalibration for leaner emissions fuels.
we offer a jet pac with tuning guide and instructions for this situation. if your missing this jet you will need a jet holder along with the jet pac.
Now I just need to find out my jet sizes.