I just repaired a customer's 3.2 engine that lost the screw....The disc went into the cylinder and got between the piston and cylinder wall...Took a big steel pin and a hammer to get the cylinder off the piston...Luckily I had a new piston and was able to clean up the bumps on the port...Never did find the screw...
The older Walbro carb screws were spread slightly sideways, the newer ones are spread by a punch in the center...Loctite works well on either...Some Tillotson carb screws use a star type lock washer..We solder the discs in the race carbs and grind the screws flush...