Hi GUys,
it's been a while since I was here last, but now I have finally got my 350 SBC to run. Everything stock, except for an Edelbrock 600cfm carb and Performer intake, double exhaust.
I have three questions:

1.) When an engine is fully assembled, everything connected, in the car and in good running condition, like if you just had everything checked. What should the timing be at idle?

2.) My engine idles very rough. At higher engine speeds it sounds better, but never really right. The ignition is almost new, plugs also, valves just newly set. What can that be?

3.) I can turn the idle screws on the carb any way I want, with no effect on the idle speed. Of course, if I set them under half a turn out, the engine will stop, but from about one turn out I can change as much as I like and nothing changes. I have no air leaks. left and right screw both have no effect.

And a few more questions:
My situation is this: About 300 miles ago, I had everything set and it seemed to be running fine, the engine has just been professionally rebuilt. I had some trouble with flooded lifters and wrong valve settings, but that is now over. But I still have to set it to about 26° BTDC to run nicely, it still has a bit of a rough idle, but if I step on the accelerator the timing goes past the 40° mark. Without a knock, even under high load. If I set it to about 10° it will idle extremely roughly, and has lower power. Can it be that different engines have different timing marks? I've seen some with the marks welded onto the timing chain cover, others have them screwed on by a bolt at the side of that cover. Can the marks then be in different places? (I.E. am I just checking my engine against the wrong timing mark?
Can you set the timing just by turning the dizzy til it runs nicest (highest revs at same throttle position) and leaving it there? That way it seems to run nicely but I get very low mileage, about 9-10 mpg in a Chevy G20 Van at 5.000 lbs , I was expecting around 13. But as I said, I can change the carb settings as i like, with no effect, the carb is new and cleaned (no stuck needles).
Slowly vut surely I think I have a problem ;-)
Thanx a lot for your help,
MadMax