Hey guys,

So I finally bought myself a vacuum gauge to do some proper idle adjustments on my car's Holley 4000 4brl. Now keep in mind, you're dealing with a 28 year old here who's not experienced in carburetor tuning. I believe I did a good job, but I figured I'd post some before and after readings in video form to see if any of you guys have any important observations.

Some things of note: I had to screw the idle screws in almost all the way before I got any kind of improvement in vacuum and idle smoothness. The right screw is about 1/4 to 2/4s turn out from closed, and the left screw is about 2/4s to 3/4s turn out. I was a bit surprised actually as I was basically able to close both screws and the engine seemed no worse for wear, I expected the engine to die from lack of fuel honestly. I had my carburetor rebuilt by Carburetors and More so I don't know how much of any mechanical modification they did to the inside of the thing.

Anyway, I mostly wanted to do this today because the car, well, has a rough idle. I seems to run smoothly for the most part but have sporadic little hiccups which you can see as vacuum dips on the gauge. After adjusting I've got them mostly eliminated and the hiccups that are still there aren't as strong as they used to and for all I know might just be part of that signature Y-block idle sound people love so much.

My other concern and question is this. Should you take vacuum readings with the car in Neutral or in Drive/Reverse? Or should it not make a difference? I ask because while in Neutral or Park the engine vacuum is right in the middle/high of the green zone 20-30 pounds. But in drive or reverse the vacuum drops into the red where it's labeled "Latent Timing" on my gauge. Is there any sign for concern here?

Anyway enough chat here are the videos:

Initial Vacuum Check in NEUTRAL


Vacuum Check in DRIVE - (check it a bit ways in, that's when it start dipping randomly.)


Vacuum Reading After Idle Adjustments