You can use a piece of radiator hose and tape. Worked for me and saved removing the cold air box on my 750.Has anyone made or modified an adapter to use the SK carb synchronizer with the 750/101 veloce air plenum. My stock snorkel works fine on the 105 and later plenums.
FWIW many very new repro Webers (like made in Spain) don't have the screw and have a press fit plug meaning there are no progression holes. The progression holes are about the size of a mechanical pencil lead and are at the bottom of the hole covered by the brass screwThe progression holes are under a brass screw cap back near the idle mixture adjustment screw. When you remove the screw cap you should see 3 or 4 small holes drilled into the aluminum body of the carburetor. When you move the throttle linkage you should see the throttle plate pass by these holes. The visibility can be helped by shining a small flashlight into the inlet of the carb.