Recently, a brother was having problems regarding the CNG settings on his city. I quoted him the method I used (it rocked my car) and Alhamdolillah, he is veryyyy happy with his car now.
Let me tell you something, City Idsi and ivtec is without any doubt, probably the sweetest car in its category when it comes to using CNG. If played with it the Pro way, it won't even let you feel that its on CNG. I give my word here.
Mine has clocked something above 216K kms by now, out of which 170K kms are completely on CNG. Never ever gave me a problem unless under special circumstances, which can be solved without much hassle.
acha, so sharing the method over here, for my fellow members. I suggest all of you tune your car according to these (DIY). It is very easy and I bet you'll feel a great great difference in the drive and feel of the car.
-Get your car's jack, start it up. When on cng, press the accelerator pedal with the jack and accelerate to precisely 3k RPM level. Not more not less.
-The jack might feel to be slipping, so once you achieve 3k, put a small heavy thing on jack such that it only stops it from slipping, doesn't press it further down, like a small piece of brick.
-After this, observe the rpm needle for several seconds and assure that the rpm isn't moving now. Fixed on a point. like 3000, 3100 something but NOT moving.
-Now, get urself a screw driver, use it to calibrate ur T bolt, not by ur hands, its not accurate that way.
-First, tighten ur main T bolt, such that rpm decreases below 1.5k (note that accelerator position is to be kept rock hard FIXED) not to be moved during this. Now the rpm will only vary as the T bolt is tightened or loosened.
-Now slowly, start opening it, when it reaches back to 3k (keep noticing the needle), open it further VERY VERY precisely, the rpm will increase further and will probably cross 3.8k.
-Check and find an accurate spot where rpm doesn't increase further. Assure the spot by tightening the bolt a little and then opening it back to achieve the MAXIMUM rpm possible by the bolt. Don't open the bolt beyond this point.
-After all this done, remove the jack and let the engine idle.
-Now, start opening the small idle adjustment screw slowly, engine will start shuddering, do it slowly so that just as the engine shudders, you STOP opening further immediately or the engine will stall. DON'T accelerate the engine to keep from stalling.
-Now start closing it slowly until the engine feels to be the smoothest. Try to find the spot where the rpms stabilize the most.
-Check this by just slightly hitting the accelerator pedal (not pressing it, sirf jhatka dena hai so that engine revs up and comes back to idle by itself) look at the needle closely, the rpm should STOP at 800 or 750 and should not decrease beyond that and come back up.
-This procedure will also help optimize ur engine to its best and the acceleration will improve a lot.
-Try this and maintain the best accuracy possible because its a game of accuracy. Bhaan bhaan wali tuning done by our local ustaads is nothing.
Human feet or hands aren't capable of maintaining constant RPM levels so use a jack and assure that pedal position does not change a millimeter during this procedure.