Once the car is warmed up it begins to spit sputter backfire and loses power

Sounds like an engine performance issue. Testing must be performed to see what element of the following is weak or or missing: 1) Fuel delivery 2) Ignition spark 3) Air coming into the intake -- either restricted or too much 4) Exhaust flow restricted Is there a check engine warning light illuminated? If so, testing can start there to find out what trouble codes might be present, aiding with clues as to where to start looking for your problem. If not, each system I listed must be tested to see if it is working properly. A well trained technician with a good diagnostic tool that has data monitoring capabilities and a shop manual to use for reference will be able to get to the bottom of your concern with little difficulty. www.repairpal.com/repair-shops

without getting too technical ,the biggest problem you are facing is the lack of obd2 ,your best bet is locate an older technician or one who specializes in this type vehicle because without obd2 the averafe technician becomes quite lost