I also have Indus Corolla 1995 (1300 cc, 12 valve engine). Engine is over hauled but still can't obtain desired average.
One good experience is switching over to Mehran carburetor. But condition of carburetor matters. Therefore obtain genuine carburetor, get it repaired if required. Main issue is mixture of air and fuel in correct proportion. Keep fuel injection at min where engine runs smooth for best average
Other things 2 check breaks and ensure they r not jam. Tappet setting, gear oil and wheel alignment.