Have been posting in Big Bolts with the re occurring problems for the engine in the 2 ton.
Details:
'48 235 (low pressure)completely rebuilt.
Modified with dual W-1 carbs and cast dual exhaust. Carbs rigged with dual chokes.
also has 700R4 transmission.
Ran well for local road tests for all truck systems.
First interstate speed test failed during a long uphill pull. blew headgasket between 3&4 cyls.
R&R head, all tests and checks found nothing, installed NOS gasket. Everything fine.
A month of frequent driving later ( heavy loads, no loads, traffic, highway) It dropped an intake valve.
Valve face broken in half and stem groove looked like it had been pulled through the keepers.
Sent head to the engine shop. Replaced everything for the dropped valve, removed all others, inspected and all new keepers. found nothing else wrong.
Found nothing serious with piston or cylinder wall.
When it happened, driver reported engine noisy, ran really rough, temperature hotter than normal, wouldn't idle, exhaust sounded funny.
Put everything back together and started engine to warm up for valve adjust and head retorque.
Problem:
Runs rough, won't idle!
Won't run at all below 1200 rpms, above that have to keep wiggling the gas pedal to pump more gas to keep it going. Will idle but only with Full choke (runs better at higher speeds). Vacuum low 14-15 at steady speeds. Temp is higher than normal, used to run at 170F (160 thermostat) now 185F.
Reset the valves and retorqued while pondering the problem.
Ignition timing good. Cam timing looks good.
Firing order correct.
Good fuel flow. Eliminated fuel quality by running out of gas can.
All vacuum lines to the manifold removed and blocked.
No external vacuum leaks detected (would have to be a big one). Vacuum advance is good, reconnected.
With throttle holding at 1200-1500 rpms running rough, used hand to completely block off 1 carb, ran smoother and faster, same with the other.
Removed manifold to inspect for cracks, etc, found nothing.
No matter what, just sounds off.

Hate to say, I'm almost out of ideas.
What do you guys have????