How Does One Adjust a Carb With a Vacuum Gauge?

[dibbons]

And what is the science/physics behind it? Thank you.

 

[krazykuda]

Turn the idle screws all the way in and then back them out 1/2 - 1 turn...

Then hook up gauge and warm up the engine... Adjust the idle mixture screws 1/8 - 1/4 turn at a time and to find where you get maximum vacuum and idle speed with tuning tach... Make sure when you finish that both sides are equal turns out...

Here's a good link on diagnosing engine problems with a vacuum gauge....

Vacuum Gauge troubleshooting

 

[67Dart273]

SET THE TIMING FIRST!!!

Then warm the engine up FULLY to operating temperature.

If these are a 'ways off' the idle speed will change. If it changes much, "diddle" the idle speed to keep it inline, so that you are making final mixture adustments AT THE idle speed you want

I would not turn them in and back out. I would start with "what you have, and just "ease" them in until you see the gauge start to drop. Then back them out both a bit at a time for "max" vacuum. Then last, just turn them in "just a touch" until the vacuum "just does or "just doesn't" drop