...One person hit on it. The very START of All this, The Ignition!
Rough Idle...Bad Idle...No Idle.
1. Points System Worn/Bad. Bad Rotor and Dist. Cap. Burned Points or Bad Condenser and/or Coil, can cause a 'Bad' Idle. Yes, a Electronic Ignition Would Smooth this Out.
2. Wrong Spark Plug, Wrong Gap, Carbon Fouled (One Suggested a V8 running 6 Cylinders.
3. Ignition Timing and Advancing curves, and More.
...From there we go to Bad Fuel, dozens of Carburetor mis-adjustments. As George Pointed Out, CAM Specs and Cam TIMING.
I must leave it there, too much to List.
I run a Distributor-Less Ignition, 4V Iron Heads, 292/588 Cam, Air Gap Dual Plane 0n 91=95 Fuel. Dumping the 'Cap and Rotor', Improves a Lot by Tons!
I LOVE the Cleveland Lope Idle 950 RPM. At 85 MPH She Purrs.
MJ
P.S. The Smooth Running was on My Desert Trip. I was running a 600 CFM Holley, Tuned to Premium, from Experience. Now Back Home, I'am putting the 750 Back-On. I run Vac-Secs on the Street, with a Manual Choke. In My Opinion Mechanical Secondaries Are Best on a Racetrack. Which brings to mind, so are Single Plane Manifolds, that do Not 'Come-On' until 5000 RPM, Still another cause for 'Poor/Bad' Idle...the Problem of Fuel Distribution, where, On the 351 Cleveland, the #8 Cylinder can become starved of fuel. That would be a SINGLE-Plane Manifold with a Carburetor. Installing Fuel Injection Has Eliminated this Problem, as in I.R. Injection. The F.I. Experts, of Which, I am Not one of, may Confirm this.
And in that regard, Aftermarket DUAL Plane Manifolds deliver a more precise Fuel Distribution to all 8 Cylinders, when Induction is by 'Normally Asperated' Carburation. Edelbrock flow bench tests, their designs, their Manifolds Work!
...One thing I need to add, concerning a 'Breaker-Points, Cap and Rotor', Ignition System. Those whom have switched to a 'Coil at the Plug' ignition system, already know this. Take a good hard 'Look' at the Physics involved, within the Distribution of the 'High-Voltage SPARK/ARC', of the Cap and Rotor. The coil creates the Arc, Grounding through a Questionable Points/Condenser, in Time to be 'Switched' to the Correct Spark Plug. Though this system has been used for 100 Years, it is Purely Wasteful, as far as, How much of the Spark Intensity is Lost in the actual Distribution, before ever reaching the Plugs. Making all of the Rotor to cap, GAP, 'Burning', purely unnecessary, and lose of potency. Now talk, rough Idle.
My suggestion, to All, is, 'Come out of the Dark Ages, and into the Third Millennium'...Get rid of the Distributor, Go to a Distributor-LESS, Ignition...You'll Realize just what I am Describing, a Hotter Fired Plug, a Highly Smoothed-Out Idle, and I'll even go further and add, Improved MPG from more efficient Fuel Burning. You will Never go Back!
Of-course, this is all 'In My Opinion', but Proven on the Highways, Best by Test!
Thank You.
MJ