Here is what u should do
1. Check any leakage of gas or any broken part or hole in INTAKE manifold or the pipe
2. Get a feeler gauge (cost abt Rs 200), buy a digital voltmeter (Rs 300)
3. Set ur plugs gap to 1.1mm
4. Check the Resistance of each plug wire. Should not be more than 25 ohms. Lower the better
5. Take along ur new feeler gauge to ur mechanic & Get valve clearance as
Intake: 0.18 - 0.22 mm (0.20 IMO)
Exhaust: 0.23- 0.27mm (0.24 IMO)
Older the engine, smaller the value
6. Dont use 20w50 oil. Switchover to 5w30 or 10w40
7. Assuming all ur sensors are OK. Check that ur advancer is connected to the Variable signal wire of the MAP sensor. Our mechanics have the habit of connecting it to the 5volt power wire.
8. Get ur timming set on PETROL
9. Get ur CNG adjusted from a good mechanic, but better is to do it urself. Apart from smooth running, the rough way of checking good CNG setting is than when u slightly block ur air intake pipe with ur hand, the rpm should decrease. If it increases, open gas a quarter turn of T bolt
10. Clean ur IACV
11. Get ur Idle adjusted to factory default i.e 750 RPM on petrol
12. Drain ur cylinder of oil by taking it out of the trunk.
13. Drain ur CNG regulator.
14. Keep the length of CNG hose from regulator to intake mani as short as possible.
15. Check if wheels move freely & are not heavy to rotate
16. last but not least GET THE RADIATOR FAN TO AUTO & NOT DIRECT< MAKE SURE U HAVE THE THERMOSTATE VALVE INSTALLED
if all this doesnt solve the problem then i have another TODO list. LOL