You should try locktite on the screw before you try anything that will damage the screws. The carb should have two holes that correspond to the positions of the two screws you're pointing to. If those holes aren't lined up, the screws won't go in the full distance, and you might have stripped the threads trying to force the screws in. If thats the case, you'll probably need to tap the threads one size over and use new screws.

For future reference, most carbs have a throttle stop screw. Normally its located on the top of the carb on the same side as the throttle arm. Loosening that screw allows you to take out the entire barrel assemble, and is a much easier way to attach a z-bend. Then just reinsert the barrel and retighten the stop screw.

Brad