Sorry this is gonna be kinda long. The story goes: about a year ago I installed a carbed 383 into my RS. The carb was a used holley 750cfm VS 3310. The holley usually had 15-18lbs of vacuum at around 900 rpms in park at idle. Timing was set at 20* BTDC. Car ran fine minus the fact that the VS where broke. So about 4 months ago I replaced the Holley with a Speed Demon 750cfm DP. After the demon was installed I took it to a shop and had them tune it. It was re-jetted and so forth. Now the car runs about 10bs of vacuum at 1200rpms in park at idle. The main problem is the car dies after its put into reverse or drive. Everything is the same as it was with the holley. Why the problems now? I capped all the vacuum lines and shot carb cleaner all around it. No vacuum leaks were found. I pulled the spark plugs and they look fine. Checked timing and it was good. Whats next? any suggestions? I don't want to take it back to the shop, cause they obviously don't know what they're doing. Not to mention the money I've already wasted.

 

Where was/is the vacuum advance connected?

 

it goes from carb to distributor

 

Okay, I'll try to be more specific.

Is it the "ported" or "timed" vacuum source, or the manifold vacuum source?

I'm speculating that it was hooked to manifold vacuum before, and now it's connected to the ported vacuum, which doesn't advance the timing at idle.

 

Sorry I didn't undertand what you asking at first. Its connected to the ported/timed vaccum source right now.

 

Try the manifold source and adjust the idle accordingly.