get the timing set, briefly it's time of spark plug current pulse for sparking with position of crank/piston which is compressing the fuel + air supplied to combustion chamber. plus timing of intake/exhaust valves.
petrol needs more air (oxygen) to burn than CNG as petrol has 7 to 8 carbons per molecule (octane from 8 carbons) and respectively hydrogens attached, more oxygen required for oxidation otherwise not proper combustion and knocking, loss of fuel etc.
in CNG we only have one (1) carbon per molecule it's methane, that's why require less air and it's greener than petrol and LPG (which has 3 to 4 carbons).
There is also function of MAP/MAF sensors as the fuel is supplied according to oxygen/air supply mainly, temperature, accelerator position etc.
that's why EFI is efficient, it injects fuel electronically based on certain inputs from sensors.
in Carby cars: mixing ratio is set by a screw behind carburetor
I feel, a good expert might be able to adjust all in balance w/o blockage. AND accelerator pull must be tightened with respect to input pressures. as w/o blocking air would be more and CNG T-knob should be opened to match the required mixture and then feeding controlled by accelerator paddle. many ways to come up....