first hand experience for you man, My Baleno 1.6 Gti consumes 600 Rs petrol after every 250 to 300 KM appx may be more..... I went to 1 mechanic he adviced emulator change n i agreed but he wont have orignal landi ranzo one so i decided to meet him on friday but due to any reason i went to LHR where i went to another mechanic for that and you ppl will be amaized to here that back pipe of petrol from tank is sending petrol after cut off on CNG, Means due to pressure built in fuel tank a back fuel pipe is sending fuel to engine, Plz check this thing too
How to check.
Start your car and convert it to CNG and remove fuel pipe that is taking excess fuel back to tank from engine side if it's getting overflow it means you have same problem and you have to change the valve at the other end in the fuel tank.......
do let me know if problem fixed and be happy