im about ready to burn this truck to the ground
now, a few days ago, it has a massive backfire which sucked the choke valve stuck in the in carb throat, so i had to pry it back open with a screw driver
and whatever happened after that i dont know, but it backfires and stalls under load now
i cant even drive the junker around the yard without it dying on me
on a side note, it revs fine in neutral, it only dies under load (when you actually need it to run)
IMO, it didn't suck the choke valve shut, it blew it shut from the bottom. I think this can only mean the plenum had a combustible mixture in it, and it caught fire from a leaky intake valve allowing an already lit cylinder under pressure to force fire into the intake and ignite it. Sure I could be wrong but I think a Compression Test or Leakdown test is in order.
As to the loss of power; if you retimed the ignition after the backfire; this would then point to a jumped chain, and a compression test would find very low compression.
But if the timing remains unchanged, and the idle-speed is not where you last set it, this again points to a jumped chain, or maybe a bent primary butterfly
But if both the timing and the idle-speed remain unchanged, then IDK, unless the low-speed circuit has failed, the secondary plate is not closing properly, or the mains are dribbling.
In any case, if it was mine, and the carb looked good,I think I'd start with a compression test, followed by an LD if the compression is really low. If you suspect a jumped chain, I prove it by checking split overlap, way easier and faster than pulling the front of the engine off.
I really hope I'm wrong, but the loss of power, accompanied by continued backfiring with throttle applied, kindof points in that direction; altho I must admit, the 16inches of vacuum has me puzzled; maybe it's just really lean or trying to burn water. Yeah that could be it!
My condolences; Happy HotRodding,lol.