If tightening the screws (be careful) doesn't do it, you can open up the housing, and there is a little block in the housing (it looks like teflon maybe?) Make sure it is dry, no lubrication in there. Many moons ago, on my other Connie, I sorta "scuffed up" that area in the housing and the friction came back. Also, check the mounting down on the carb (#3-4) and make sure everything down there is good and tight.
I think it's been checked before, the little block in the switch housing can be removed, but it is not available seperately for purchase, you have to buy the whole switch gear.