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I have a 350 that is running a little rough at idle (flutters a bit, dies if left running at idle when warm (rarely, but sometimes), etc), just doesn't sound *quite* right.
The Distributor is an HEI unit with the builtin coil on top.
here's the details:
- I have checked the order of the cables (18436572) with the block and they are fine.
-  Plugs are new Bosch Platinums.
- New Edelbrock 1406 Carb (old one was a Holley, same problem)
- I've run a timing light against it, set to ~10 advance)
- I've run a Vacuum Test Gauge, comes out to ~16 inches regardless of RPMs
- PCV is plugged to the Carb
- Vacuum Advance goes to Manifold, Carb nozzle is plugged (for the vacuum advance line)
- I have no exhaust ... just headers for now. This rig is a build up.
I played a bit with increasing/decreasing the timing by turning the distributor, but she honestly sounds the best where she is from my novice perspective.
- I don't have a tach, but I figure by 'sound' she's at about 800 RPMs or so at idle right now. If I bring her down any more she dies.
- I tried to use the Vacuum Gauge to adjusy the mixture a bit. I had it using a T adapter and having the vacuum hose from the manifold that goes to the Vacuum advance on it. I tried to see if its the mixture, but the gauge didn't change at all when I screwed the two mixture screws all the way in or out. The motor does make a change in sound, and when all the way it out runs VERY rough for a second and dies. When all the way in, you get lots of black/rich smoke from the headers and through the carb, but it stays running. I have them about in the middle right now, the exhaust smells lean and fairly good right now.
- She backfires here and there when womping on the pedal. Fire shoots out of the headers, etc.

Anyway, I don't know where to take it from here. Is there any effect that having no exhaust could do? Also, is it possible that not having a tach means my ears are wrong and that I actually could be too low in RPMs? I mean, she typically runs better at higher RPMS.

Thanks in advance for any ideas on what to try next.  

I have the same problem with my stock 350. I've changed the carb to a new holly 650 and still the same problem. I turned the mixture needles either way and still has the same problem. Could you tell me what you did to solve your problem. E-Mail me at shawnshoop@hotmail.com. Thanks!  

How many miles are on the engine?
Maybe you have a burnt valve.
Have you done a compression check?
Could be the carb needs tuning also although edelbrock carbs are usually good to go right out of the box.
Good luck

Al  

First thing I would do Is check fuel pressure concidering the compression check has been done. Another idea is to have a flamable spray such as carb cleaner handy. Just as the engine begins to die, with the air cleaner off, and with extreme caution (in case of BACKFIRE) spray it briefly into the carb . If it tries to recover you know you have a lean condition, if it continues to die it is loading up.

Hope this helps. let me know  

AND, to go along with above ,With no exhaust it could build exhuast in the engine compartment and will cause a rich condition since the ehaust has little oxygen