Chevrolet Repair: de-carbon engine, oxygen sensors, co emissions

Question
1991 S-10 4.3 250,000km t/b inj.
Recent E-Test reveals rich running and carbon buildup. One suggestion:MOTORVAC  (big bucks)
Another thought: GM throttle spray cleaner and a can of top end cleaner (CARB-OUT ?)along with some injector cleaner in the gas.
Oh,bye the way, would carbon stop my cats from treating the co emissions? My HC is below the max,however. (go figure)
What would you suggest for a senior citizen to try to rescue the (probably) choked (or coked) up engine?

Answer
Burnt gas creates higher hydrocarbons then unburnt gas.
Unburnt fuel can cause more problems than I care to think of.
I am sure your check engine light is on.
Have a mechanic check the EGR valve, then check the oxygen sensors.
Yes, carbon will slow the process of treating the exhaust gases.
But, then again, so will pure gas.