Too many unknowns? could be the tuneup, or the way it was built?
I's start with the basics, pull all the spark plugs and inspect them.
Make sure the airfilter lid is not too close the the fuel bowl vents (I think the 850 has angle cut vents, but it easy to check.)
Check all the plug wires resistance and insulation (if in doubt of their condition, get new ones.)
check cap/rotor/rotor phasing/ignition coil.
Check compression and leakdown test all the cylinders.
Pull valve cover and inspect rocker arms and pushrods. Check valve lash or lifter pre-load if hydraulic. Measure the cam lobe lift to get an idea of the cam size.
You may be able to get a small degree wheel in the car and even check the cam install centerline and opening/closing events to see the duration size of the cam.
I would think with 210 to 220 PSI the cam is either pretty small or way advanced? If you have a visual inspection probe you might be able to see through the sparkplug hole to see if the pistons are flattop, dish or dome.
Check fuel delivery at the carb. Connect a long fuel line and place the end in a 5-gallon fuel can, and time how long it takes to fill the fuel can.
You should get at least 1-gallon per minute (60 gallons/hour.) If you have a fuel pressure gauge check the maximum pressure, you can also "T" into the fuel line, and add a restriction (clamp on hose, etc) after the "T" and re-check the fuel flow with some pressure.
If the fuel flow starts out good then slows down, the fuel tank may not be venting. Remove the filler cap to vent, and re-test.
If all that checks out, and it looks like the carb is out of tune, you may want to go to tune on a chassis dyno with a wideband O2 sensor.
The Carb shop did a good job on my friends '68 Baracuda. I have also used Dyno Pro, but made the changes myself.
