Sounds like the exact same symptoms my car has. Runs OK when cold, and very badly - bucking, sputtering and dying - when warm.
My first advice (based on recent experience) is "
do not touch any MFI adjustments". Chances are there is something more basic at fault.
I don't know yet if the bad fuel return check valve is the cause of my problem, but I have high hopes. I've heard from others now who had failed check valves, they experienced similar symptoms. Mine will be here later this week.
In the meanwhile, it might be worth taking a look at the one on your '72. See if is is sticky, or stuck partially open like mine was.
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