Missing at cruise. 5

Lets take a moment to consider what a "miss" at 3000 rpm could be.
For some reason the fire either went out, came late to the party, or never got started in the first place.... right?
You can tell which, by the severity of the "miss".
Why this happens is no mystery.
This happens if/when, the fire didn't go the way it should.

Why it didn't go the way it should, can only be for a few reasons. It could be because;
1) the spark is too cold (not the plugs heat range) rather the spark is just too weak to light and maintain a decent sized flame-kernal, and so, as time passes the kernal sputters and dies, with the majority of the fuel going out the tailpipe unburned. This can be band-aided with a multi-strike that just keeps banging away over and over. The thing about this is that, none of the sparks following the First Strike are timed right. So then, as your rpm exits the Multi-strike zone, now you are back to a standard CDI triggered kettering-type ignition. And if you are using an E-core coil, they are almost notoriously under-amped.
2) the above happens regularly if the mixture is too lean. In this case, the fuel molecules may be too far apart to maintain the flame, and so the power output becomes lower than the cylinders around it..
3) the above also happens if the AFR is too rich AND the mixture is NOT properly atomized. In this case, the larger molecules just get ignored.
4) in both instances, this situation can be aggravated by the shape, size, and temperature of the chamber, and can be severely aggravated by the headers, and most especially by the lack there-of.
5) the solution to most of this crap, is to run a hi-amperage coil, and to start the flame-kernal earlier, so that the fire has more time find fuel to burn, before the piston gets to be too far down the cylinder.
Cuz I mean think about it
For optimum energy transfer from the pressure of the expanding gasses to the crank, aka, peak cylinder pressure, the pressure needs to occur at or near a specific crank position. All your timing systems are designed to hit this position, as often as possible, under the most trying circumstances. This crank-position is said to be 25 to 28 degrees AFTER TDC. I showed you how to find it in a previous post.
Did you catch the word AFTER?
At this crank position, the piston is already running away from TDC, and so if the fire is late to the game, it manifests as a miss because the power is down on that cylinder. If all cylinders are down equally, then you wouldn't feel it, but your fuel-economy would take the hit.
So then, when cruising, it MAY take 45 to 55 degrees of advance to get ALL the fuel molecules oxidized, at the correct time.
All of this gets aggravated by;
a dome in the chamber, acting like a dam,
a large open-chamber design with lots of surface area for the fuel to stick to, including a dish in the piston or the crowns being below the deck, or aluminum chambers sucking the heat out, or
alack of squish to homogenize the mixture, or
spark plugs too far away, or gapped too large for the coil's power, or
The carb's inability on the cruise circuit to supply the finely-atomized fuel, or
the fuel sticking to the relatively cold intake manifold runners, or the plenum, then tearing off in large patches, too heavy to burn, or
the overlap cycle, with headers, being particularly aggressive, or if no headers, then exhaust gases pushing up into the plenum on the overlap cycle, messing with the AFR. The carb doesn't care which way the air is going, if it is going past the transfers and idle discharge potrs, in any direction, she dumps fuel into it. The overlap is in charge of the beginning of the intake stroke. So if log-manifolds are used on a 250* @.050 cam which is gonna be well over 300/310 from seat to seat, and the overlap from .008 to .008 tappet rise is likely to be over 80/85 degrees ..... this is plenty of time for log-manifolds to drive EGR up into the intake.... plenty of time.
>and finally, the wildcard, is detonation, or in this case, more likely would be Pre-Ignition. This is when the fire starts waaaaay to early, and the rapid rise in cylinder pressure drives the piston back down the way it came, and you feel it as a loss of power, aka, "a miss". Now, pre-ignition can be a bit of a mystery, as to why it occurs but the fact of it can usually be traced to, something in the chamber being hot enough to light the mixture before it's time. It could be the plug, or the edge of the cylinder protruding into the chamber, or the fire-ring, or waaay too much compression for the gas , or a faulty octane-rating, or some particularly hot or glowing item in the chamber, or some combination of these.
This has to traced and eliminated else the engine can destroy itself when detonation moves in behind it.

In any case, the point is that, cruise timing is sorta critical. and
I can say with confidence,that
IF your engine is NOT sick,
AND if you have a decent coil and the right timing,
THEN, you can cruise with a pretty wide range of AFRs ,
and never experience a miss.

but you know, if one runner is sucking air, none of this matters.........

I once installed a modded for fuel-economy Holley 1850 on my 367, for a specific 10 hour cruise, and was amazed at the fuel-economy it achieved. But, I could vary the timing, on the fly, from the driver's seat, with the adjustable timing module, so it was always exactly right. As it got leaner, it required more throttle to get the required fuel to maintain speed..... and more and more timing. Eventually it could not make enough power on the cruise circuit to maintain speed, and no amount of additional timing could find it. But;
not once did it misfire.
I run a pretty basic ignition system. Just an old yellow sq-top Accel Super-Coil.
It gets battery power from a relay, turned on by the ignition switch, and is triggered by the Opto-Timer's internal amp. That coil is simply amazing, especially for the money it cost me. It was new in 2002.