Back in the 1970s, the local dealer had sold many 273 2bbl Belvederes to some elderly ladies. A nice car that met their needs. The only problem was that they only drove them short distances in-town, which meant they usually stayed low-speed most of the time, which also meant short trips where the automatic choke seldom would get fully "off". The result? Coked-up exhaust heat passages as shown. The fix, at that time, was to remove the intake manifold and chissel the accumulation out so the heat crossover would flow hot exhaust again, which also meant the choke would open again. Never had that issue with a B/RB engines as they usually ran hotter, so no similar issues.
When I got my '80 Newport 360 2bbl, I learned about "LA motors run cooler than B/RB motors" as in almost every winter season, when the idle got a bit unstable, I discovered that the pcv line from the back of the carb (Carter BBD) would sink lower as it made its way to the pcv valve AND was heavier in weight from moisture accumulation. The top of the oil dipstick would also get some white moisture accumulation on it, too. The fix? New pcv hose and clean the pcv valve. A simple and easy fix. Never had to do that with any of my 383s. AND, this was my daily-use car back then, so it was getting a good bit more than 10 miles/trip use.
To me, rebuild the carb or remove the LB system as the LAST resort. The carb usually is not that gunked-up to really need a pull-apart situation, by observation. I also suspect the LB system is not the issue, either. Just put some quality spark plugs (even Iridium NGKs?), put some carb cleaner additive in the fuel tank (and use some good carb spray to spray the venturi cluster with), change the oil and filter, and go from there. In other words, don't presume that something needs to be done just because others might claim it might need to be. Cap, rotor, and wires are only age-related items and don't summarily need to be replaced, too, just scrape any deposits from the inside of the cap and the end of the rotor. KEY thing is that the parts you replace the existing parts with could well be inferior to what you now have!!! Unless the plug wires are stiff and crinkly, leave them be, too.
IF the LB system is really causing the issue (from accurate diagnostics), then do the replacement situation with quality parts, provided the computer is not the issue. With 1976-77 model year replacement parts (electronic ignition and carb). Just to make sure the carb and ignition are calibrated to work together, rather than not.
Just some thoughts and experiences,
CBODY67
