Nothing big.... i went to suzuki 3S dealer ship many times telling them that when driving on CNG i have to turn off the AC to get some pickup bla bla and they always tune it up and its of no use i used to take my car at 3S every 5000Kms after 30000Kms i quit going there instead i went to my machenic and told him the problem he just tuned the ride him self with desi tareeka and since then my alto is good in running and i m satisfied with it.
It has stock plugs in it first change was done on 50000kms then on 100,000 Kms and car is now at 105,000kms and still running as new. I use shell (blue bottle) oil in it and i mix a STP oil with it 3 liters shell oil + 1 stp bottle. I change engine oil + oil filter (VIC) + Air filter (guard) every 5000Kms but i daily convert it to petrol when parking at night and after driving 1 Km on petrol conver it to CNG again thats what i have been doing with it for the last 4 years. Its a 2004 model and belive me its better then the new ones.