Red Hot Exhaust Manifolds!

1985 chevy G20 5.0L 4bbl quadrajet 3 spd trans.
ok the thing bogs under load and pops and exhaust comes out the carb. i did plugs wires cap rotor wires and fuel filter. then drove it with the doghouse off and noticed the top of the Y pipe and both manifolds getting cherry red hot. so i figured it was a plugged cat. replaced the cat and the problem is still there. i cant check the timing because when i unplug the 4 wire connector the thing won't start. when i unplug the 4 wire con. while van is running it dies. as of now i am stumped i have never seen manifolds get that hot before without any exhaust restriction. any suggestions??

sounds like timing to me.

try a compression check. See if you have a bent valve.

Its running lean way to lean check the carb it might need rebuilt

Fireplug is correct. My answer would be the worst case. Start at the fuel filter on the carb. (inside the fuel line inlet fitting)

Seen this more often than I can remember.
I hate to say it but your going to have to replace the camshaft. The rear lobes are wore down ( weak spot on GM engines of that size) You can verify by pulling off the valve covers and cranking the engine and watching the valve train lift.