I'm into another round of tests which is going to include making a switch from ported vacuum to full manifold vacuum for my advance.
My schooling (and old schooling I should add) has always said to keep the vacuum advance disconnected while setting the timing but it has me thinking about how it will affect the idle mixture.
When using ported vacuum, it's a non-issue as there's no additional timing supplied at idle so the mixture isn't affected. With the full manifold vacuum pulling in as much as or more than 15 degrees it's certainly going to have an effect on the mixture quality and adjustment of the mixture screws.
What's the consensus on setting up the mixture with full vacuum advance applied?

 

I used to run manifold vacuum to the vac advance on my old '65 GMC w/283.

1. Set the timing with the vac advance disconnected (plug the vacuum side of the hose).
2. Re-connect the vac advance.
3. Set the idle speed.
4. Adjust idle mixture.
5. Done.

 

you want to set the mixture with the engine in the same state it will be driven in- so do it with the vacuum advance hooked up with the engine up to temp.. but not only up to temp, but also heat soaked like it would be after a long drive and in gear if it's an auto trans..
you will be able to get some amazing driveability, throttle response, and fuel economy out of it just by turning those screws if you work on it for a while..

 

This is how I went about setting mine. Only difference being I didn't need to make any idle speed adjustments.

 

Pretty much as I figured. It'll be interesting see how much of a change there might be in idle mixture adjustment with the spark advance at 30 rather than the static 14 I have now. I know the engine will like it.

Good point. There's a big difference in the mannerisms of the car with the changes in operating temperature. I can keep the car at 165 steady state cruise because of the 160 thermosat however it'll creep up to 200 when idling in traffic on a hot day. (Great rad, poor cooling fan. I need to install the dual fans I have on the shelf). Thinking about it, with the timing advanced with vacuum, I may idle a little cooler.

I have a Barry Grant Speed Demon carb with the Idle-Eaze feature. Whatever the idle speed might rise to, I should be able to tune it out and leave the primary throttle blades seated with the correct amount of the transfer slot exposed.

 

I apologize for replying to a ten year old post but I've never heard of anyone adjusting air/fuel with the vehicle in gear. I'm asking because most vehicles that I have owned have a higher idle in park/neutral vs shifting into gear while on the brake. Wouldn't setting the mixture at a lower rpm have a negative effect on the vacuum reading? I'm somewhat new to the carburetor life & I'm the type of person who is always open to outside the box ideas that have more benefits than flaws.

If anyone can answer this it'd be greatly appreciated & once again my bad for replying to a ten year old thread.

 

Sometimes resurrecting an old thread is a good idea if the subject stays relevant.
Seems to me it still is.

This was common practice back in the day and still an effective way of getting an accurate idle.
Since we don't drive in park or neutral, idle speed (and subsequent vacuum) was set with the wheels chocked and the transmission in drive.
If you take the logic of the park/neutral idle speed being higher then the opposite is also true. Setting a comfortable idle speed in park will result in too low an RPM in drive.
As with any carb tuning and spark advance, it's always a back and forth deal. One change here affects something there and so on.
It took me an age to dial in the manifold vacuum advance while maintaining the correct throttle blade position.