in between my avg also got bad maybe mostly because setting used to keep getting out, n result was 11.5km per kg
so i got the cng kit n cylinder serviced
they just inverted cylinder n hardly any oil came out of it, from kit they said some half cup oil came out, rest they cleaned it with petrol like they clean throttle body
after that he set the lpg setting, all done from my own mehanic
after that pick seems little less but avg seems good, i havent really finished lpg since but with ac sometimes, it crossed avg of 13km per kg n still was going when i got lpg again
on my last refill, lpg guy told me that some 20 cars came on that day n mostly after 2pm, i guess it was those guys who couldnt get cng n thought to shift to lpg 
getting the service done was good as ever since setting are fine, no issue of car turning off etc n same setting n good avg 