get the carb serviced, change spark plugs, replace air filter, replace engine oil and oil filter, get the tappets adjusted and dont forget to replace the CB Point and Condensor. The gap of the CB Point must b 0.40mm while on position of the cam. after all these, get the timing adjusted according 2 petrol and cng.
thats it... INSHALLAH this will solve ur problem........
automobile technician (TOYOTA SOUTHERN MOTORS)