Q: My engine idles real high and rough and when I try do drop the idle down, it dies. What gives?
A: This is usually caused by two things. The vacuum advance being hooked-up to the wrong port on the carb or a big vacuum leak somewhere. A vacuum advance always gets hooked-up to "ported vacuum" which is a port somewhere on the carb above the base plate. On Holley's, it's on the passenger side, halfway up the side of the carb on the metering block. DO NOT hook-up a vacuum advance to manifold vacuum. If you can put your finger on the vacuum port and you feel suction, don't use that port! The other thing that could cause this is a vacuum leak. You can usually find vacuum leaks by spraying carb cleaner around the outside of the carb and around the intake manifold. If the idle goes up when you spray it, there's your leak. Another way to check for internal leaks, like internal carb leaks or leaks under the intake manifold (in the valley) is to hold your hand over the top of the carb, blocking-off most of the incoming air. The engine should immediately die. If the idle goes up at all, you've got an internal vacuum leak somewhere.
