Stumbling Slant --what is left??
Interesting: the new plugs with barely 30 minutes of idling on them are showing carbon black. The old plugs that came out were fairly black, too.
except that this thing misses at all RPMs and throttle positions.
IMO
Your miss is coming from the ignition system, in response to the sooted up plugs, which are leaking voltage to ground. Fix the sooting and the ignition will get back to business. A missfire like you describe; speaks directly to incomplete combustion.
We are conditioned to think that;
rich means too much fuel. But
rich can just as easy be not enough air.
Now, lets just talk for a bit;
You say the compression is about 90psi.
90psi by itself is not bad. But;
in your case; the same rings that only make 90psi, are not "sucking" very hard on the intake stroke, so it takes a large amount of piston-travel, to actually get the atmosphere interested in entering the carb..... where it finds the butterfly almost closed. So it's real lazy about it. So then, when you open the throttle, the already lazy air stream finally gets moving, and pulls fuel. By this time, the piston is slowing down getting ready to stop, turn around, and go back up on the compression stroke. So the "suction is decreasing rapidly. Hopefully the valves close and seal, so that the pistons cannot drive any of that just barely inducted mixture, back into the intake. Which would upset the next cylinder in the firing order.... and maybe another.
What this means is that for any given speed, the throttle always has to be opened further, to get sufficient air, to maintain that speed. It also means that to accelerate, the throttle will again have to be opened further than is "normal", to get the required air.
Now; because of the overly large throttle opening, the vacuum advance has shut off, Leaving your timing retarded.
So now, not only do you have a slow moving column of air, arriving late to the party; but when the fire finally gets lit, the piston is well past where it ought to be, so the engine is down on power, so you open the throttle even further to get the power you need.
But because the finally burning and expanding gasses are chasing after the piston, the gasoline molecules are having a real hard time finding oxygen to react with, because all the molecules are so far apart and getting ever further apart with each passing millisecond. And so, a lot of fuel just never burns, or never burns completely, inside the combustion chamber, and a lot of it finishes burning in the exhaust manifold. Of course that means the exhaust system now has pressure in it, and the pistons have to pump that down to the tailpipe. Furthermore,if there is any air getting into the exhaust manifold or the downpipe, you may at times have multiple afterfires at various rpms, as the unburned gasoline molecules find fresh oxygen to react with.
Ok so that would be the scenario if the ring-seal is bad.
Now, throw a restrictive exhaust system into the mix, and you get an under-powered, lazy, after-firing, plug-fouling POS.
If your engine was designed to only have 90psi, and your rings and valves were working perfectly, the engine would run just dandyfine, but you would need more than 225 cubes to propel your car decently.
Ok no more talking.
Your engine has exactly one right time, measured in crank-degrees, for all the air and fuel to have finished reacting, and the hi-pressure gasses to be pushing down on the pistons. IDK what it is for a slanty with a 4.125! inch stroke, but I do know how to find it at idle, and at cruising rpm, and at WOT. All your timing systems are factory engineered in an effort to start the fire at the right time, to achieve max pressure, at the right crank position.
In order to set your starting point (base-timing) in relation to the piston, you first need to know exactly where TDC-Compression is. Your balancer has a mark on it to help you, but unless you prove that mark is true-TDC, you cannot know how accurate it is. So this is job #1..
Job #2 is to set the True timing.
Job #3, is to Measure the vacuum, and interpret the behavior of the needle under various conditions; which will reveal a lot about the condition of your rings and valves, and even the exhaust system.
Ok so back to the toolbox and Happy Wrenching, lol.
BTW;
I wouldn't trust those plugs in the condition they are in. I know they are brand new, but that soot is guaranteed to drop your coil voltage, and if it drops too low, then you get missfires.
Speaking of which, your points have to be gapped pretty close to exactly right, and they have to be clean; oily points are trouble. And the point-gap has to be the same on each of the six cylinders because the gap controls the timing. If the gap is changing while running, then so is the timing. Furthermore, a bad condenser will sometimes do what your engine is doing, but IIRC, you already replaced it.
