The jet screws into a tube called the jet needle...
It's slipping up in the hole...
(you can push it down from inside the carb throat,.. or, as you were, catch it with a longer screw and pull it down... then once it's down, don't push the main in, and then try to screw it...  
Instead,... hold the main gently in position, and start turning it, to catch the threads... then, the main will pull the needle jet down and hold it in place)....
...(usually, just removing the washer will allow the main to catch, and you can pull it down, then reinstall with the washer in place)...
... Don't forget the washer that goes on the main jet... it needs to be there...
...
Most carbs are like this (some others have the needle jet pinned in place)......sometimes you don't notice, because the main catches the needle,... but they can occasionally get pushed up...
See part no.11...

Get Yoda on it,.. Rob... ...
If you can catch it with the screw,.. you can catch it with the jet...
.... if you absolutely can't... you'll have to pull the carb, and bench it, so you can get yer' finger in there, and forcefully push the needle jet down, and hold it, while you get main to thread...
There's the easy way, and the hard way,.. but there ain't no other way...
... with some gentle focus,... you can usually coax the threads into mating...

Best luck,
Serow