I agree with ericsB210, this happened to me when I was starting up my new engine, same Weber. It ran beautiful until it drained the float bowl. It turned out the FPR was faulty and not letting enough fuel through. Once you've started it up and it dies, rip the carb top off and see if there's any fuel left.

I think your main problem is still there; fixing the vac leak probably fixed a different problem created by removing the emission gear.

Re idle: You should screw your idle screw all the way in (not too hard or you'll damage it) and then unscrew it 1.5-2 turns; that should get you started. Once it's warmed up screw the idle screw in till it starts to run a little rough (too lean) then unscrew it till it starts to run rough (too rich). In between those two points will be somewhere close to right. Grab a vac gauge if you want to set it up a little better.