Electric tape did not work well, but piece of sponge did work fine. Just something put to hole to make it isolated. There is other bit too, adjustment screw should have O-ring in it, there is kind of 'neck' in screw for that, it is important bit that does part of the seal and also helps screw to stay on place.
Oh, that is of course assuming you have Solex carb, I just remembered that they came with other carbs at early years.
edit:
This is mixture screw in Solex, deep in a hole:
This is busted idle solenoid o-ring, but also at lower right of photo you can see idle speed screw and spring in there:

full image
http://jtbo.pp.fi/images/360/cisac2/album/IMG_3190.JPG
There is 93 photos from carb that I took when I did put it to pieces first time ever, so I know to put everything back correct way too:
http://jtbo.pp.fi/images/album/360/cisac2/album/
Photo 94 shows location of idle speed screw and on that photo at top right is choke adjustment screw.
Might be helpful to know or not, but makes it easier to tell what I'm talking about when one can see it from picture, my words can be completely wrong ones to describe them

Volvo 360GL -88 -under restoration-
Volvo 343DL vario -81 -running-

Volvo 240 Diesel -83 -undecided-
Citroen ZX Dturbo -97 -daily-

