most likely the PCV valve is choked that is 1 reason for blow-back feel when filler cap is removed. 2nd the auto choke may be disconnected which remains active while engine warm up, do ask the owner for maintenance history. engine oil, transmission oil clutch work etc etc. If the vehicle suits your budget take it, you may need to spend another 10-20000 to achieve the desired performance., what is suspension & steering condition.
@syncview @argtr65