I'm still trying to troubleshoot my idle issues. Two nights ago my car stalled out at a stop sign due to idling to low (600 rpm in Gear and 1100 in park). I ran and bought a vacuum gauge the next day to find I was only getting 9-10 inches of vacuum in park. After tinkering with the idle mixture screws on my Speed Demon 750 (DP) I got it to idle at around 1200 rpms in Park and 900 in Gear. I also got the vacuum up to 12.5 inch to 13 at idle in park. That was after adjusting the screws back and worth watching the gauge till I got down to 1/8 turn adjustments with each corner matching to verify the highest vaccum was reached.

Is there any way I can get my idle speed any higher or is this where I should be at for the cam size? I don't really want to use the idle set screw since I have my transition slots set about perfect. Front float is 1/4 way up the window and back one is set dead center of window.

Specs:
SBC 383
750 DP Speed Demon Carb
Victor JR hand ported intake with 2" 4 hole spacer
210CC Race Ready AFR heads (76cc)
10.1:1 Compression
1.6 pro mag rockers with stud girdles
Solid roller cam (XE280R) - Duration at 050 inch Lift 242 int./248 exh.
Valve Lift with Factory Rocker Arm Ratio 0.570 int./0.576 exh. lift
Lobe Separation (degrees) 110

Comp Cams Solid Roller lifters with rev kit
Complete MSD System

I should also add I have 19* lockout in vacuum advance distributor so my initial timing is around 16*.

 

It's OK to have the transition slots closed from the recommended maximum. You should be able to get a cam that size to idle at 750rpm (or less) in drive. If you're happy with the idle mixture quality and vacuum then turning down the idle speed screws won't affect your drivability.
I found that a wide band O2 gauge is the best tool (along with a vacuum gauge) for tuning carbs. My vehicle (and others I've worked with cams larger and smaller than yours) tend to run a little better when the idle mixture is slightly rich. Seems to provide a slightly better transition when pulling away from a full stop.

[I should also add I have 19* lockout in vacuum advance distributor so my initial timing is around 16*. ]
Does that mean you have 19* mechanical advance and 16* initial for a total of 35* or do you run full advance all the time ( like a race only engine)?

 

16* initial with 19* vacuum advance so 35* degrees total.

meaning 16* at idle and the distributor being vacuum advance will start adding timing as rpm increases for a total of 35*. I plan on running this car on the street mainly so I wanted it have good street manners.

 

I think you'll find that the 19* comes from the mechanical advance mechanism in the distributor. That will be rpm related as you point out.
The vacuum advance will provide additional advance over and above the mechanical advance. This is controlled by engine load by way of a ported manifold vacuum source. It may in the order of 10-12*. At highway cruise speeds there could be more than 45* of timing available. (16+19+10). That's not entirely a bad thing especially for a street driven vehicle.

 

Guess you're right. I looked the instructions it says up to 10* from vacuum advance while part throttle driving and 15 lbs of vacuum. (Which I wonder if that is a typo and should be 15 inches)....

Anyways I raised my front float level to the middle of the window and readjusted the idle mixture screws again I had ~13 inches to 13.5 inches of vacuum at idle in Park. I plan on rechecking it again some night this week. Idle is still pretty loopy in gear, kinda sounds like the motor is about to die but it doesn't. Probably due to the big solid roller cam, ported intake, and the 210CC heads with 2.08 valves.

I did manage to put 10+ miles on the car last night so it looks like I'm actually making some progress.

I also managed to find the #2 spark plug had a bad insulator in it. It was sparking out onto the threads every time it fired. I doubt I would have found that without all the late night vacuum tuning in dim conditions.

 

15LBS TYPO

 

You should double check your total mechanical advance. Determine how much you have and at what rpm.