Idle mixture setting with Vacum gauge am I doing it wrong ?

[SoCal250]

Hi gang I wanted to know what HG is right when you ajust with a vacum gauge , I am familiar with ajusting mixture Jets without a gauge , I had a Harley and a few older cars years ago I always turned them in slowly till the idle started to stumble then backed them out slowly till I can hear the rpm increase and tried to get the highest rpm at some point it will start to stumble again then I would turn it back in and try to be right in between .
I had a vacum gauge I took off my brake bleeder and used a hose to the back of my carb I was at 40 that was the highest vac I could get before it stumbled or stopped climbing . It was not a HG gauge just a plain vacum gauge I am running a big 2bbl 500 cfm Holly 4412 with a spacer on my 69 390 I see the HG vac gauges only go up to 30 ? Also is turning the mixture screw in lean or rich ? Thanks for the help .....

[1972hiboy]

I have only used a vac gauge in conjunction with other tools to help tune in carbs. Ideally you set for highest reading. I like to go by feel,sound, and if i am in doubt a spray can of brake kleen to shoot in. If you are lean, a shot of brake kleen with raise rpms, if you are to rich it will drop rpms, you find that spot where it just starts to drop off if you give it a snort. But most of the time I go by sound, feel, engine behavior and drivability.

[sargentrs]

[tnlprt]

18 to 22 inches of vacuum is the most you should be able to pull

15 to 17 is most likely what you will end up with in a Stock engine in good shape

Timing must be on the money

Adjust mixture screws until you achieve the highest vacuum reading

Done

[WarEagle]

Try hooking the vacuum gauge to a manifold vac port. It might be different than your carb port. 40 HG doesn't seem correct. Mine reads near 20 when properly tuned.
Yes, clockwise will lean the idle mixture only, not mixture under load.