there is one - the picture you posted on your thread for the ac idle up has a screw adjuster which you can turn to adjust the rpm of the engine with A/C running. adjust it so that the engine idles at 900 rpm with A/C (its factory spec - dont listen to the ustaad mechanics on this)
your car will never achieve more than 90 km on one full load of CNG - you should install the thermostat and correct the fan wiring and make sure the distributor is working perfectly - warm engine (82C minimum) with all items in tune will increase the CNG mileage.
btw the coolant you are using is useless - its water with some colour in it, use a proper branded coolant in it.
btw - your car is 1986 model - 86 had the nicer seat fabric and the fuel/temp gauges that have needles pointing outwards - it also would have a golden valve cover and also have a build date - usually between october and december 1985 right on the silver plate on the left of the car.