I have a 2004 cultus bought it used in 2010 and i had almost the same problem as yours.
As for the self hanging u need to get the self checked...i got mine checked and they changed a cog or somthing in it and it works fine.
Your fuel pump pressure needs to be checked and ur fuel pipes might need to be changed...in my case the fuel pump had gone bad and some the lines were leaking petrol
U need to get your carb tunned by an expert and remove the air blockage in the air filter pipe that they put there when using cng .
I dont know the exact name of the part but there is a small things attached to carb to regulate fuel ..its has a thin membrane that part often leaks and in my case it use to throw half the fuel in the carb ...rest was wasted .
While your at it check the fuel filter and most probably the fuel tank is rusted by now ...get it cleaned and change it if you can.
The cars engine timing also needs to be checked .
Hope this gives u an idea...i had all of these problems and took 6 months to slowly track the problem and solve it