by dabraze » Wed May 19, 2010 10:36 am
Hopefully you'll get this in time to help you.
I haven't personally seen the K&B .18. It appears to have an airbleed carburetor, rather than the more common (these days) twin needle.
The airbleed works just like the idle needle, however it works backwards. To lean the idle, back the screw out, to richen it, screw the screw in. If you look closely at the carburetor, you will see a small hole below the idle set screw. As you screw the idle screw in and out, you will notice that it covers and uncovers the hole. To lean the idle mixture, you UNcover the hole, making it larger, admitting more air, and vice-versa to richen it.
The air bleed type of carburetor is more primitive than the twin needle type, but works perfectly well; you will also find that it is a lot less sensitive than an actual idle needle valve. Make sure that the tip of the screw and the air bleed hole are clean and free of any debris.