Thanks to rustbuckett's pic, it looks like # 25 is the power valve?

I'm guessing the power valve is either stuck/worn out/ruptured?

Here are the symptoms (also mentioned in another thread):

runs fine when cold/warming up.

When operating temperature is reached, there is a severe bog/hesitation/lag immediately after throttle tip in, when stepping on gas pedal. If you push farther down on the gas pedal quickly enough the engine will start running with a huge lurch forward.

It will pull away initally from a stop sign/ resting stop fine, then bog down at appx 900 rpm. Usually it will die, restarts immediately.

We have replaced:

accelerator pump
spark plugs/wires
dist cap/rotor
fuel filter
fuel pump
ignition module
coil
ballast resistor
pcv valve
egr valve vaccum line pulled/plugged
vaccum line to canister on heat riser pulled/plugged
distributor advance vaccum line pulled/plugged

timing verifed as to factory specs

carburator misture/idle adjusted numerous times.

timing verified