[Resolved]  Maruti/Wagon R LXi — low fuel efficiency (average)

I bought a Wagon R LXi last October (2007) from Ratan Motors Mumbai. I had a gas kit installed at Ratan Motors itself immediately on booking the car. I was entitled to three free services by maruti India - 1 month, 6 months and 1 year. I had my car serviced all the three times at ratan motors - Mumbai, Chembur (Deonar). The first two services were satisfactory and the car was running fine. But the third free service has ruined my gas fuel efficiency completely. I get an average of 6 to a maximum of 7 over last 3 months on LPG. But the petrol efficiency is 11, so no problems as such with petrol. My car was sent to Ratan Motors thrice in three weeks after the third free service. The engineers over there have changed my filter, modified the settings and have done all they could, yet my average hasnt improved which is unnacceptable. i hope to someone here can help me out !