The absolute best, most productive, and wonderful modification you can make to your 4160 is to add a small adjustable set screw to the base of the secondaries (replacing the one that's already there) that will allow you to control your idle via that screw while leaving the primaries perfectly set in the transition slot. Here is a pic of mine and here is a lengthy thread where I help someone get his 4160 absolutely perfect.
Best Way to set the idle mix on a 4160
