Specific to your original question ?How to Adjust CNG throttle?, I think you not been able to put your question properly but anyway let me provide some help. Apart from low pressure solenoid valve adjustment and Idle RPM valve, RPM and static rpm lot depends upon type of venture installed on your vehicle.
Once, you put your foot on accelerometer then throttle body opens, which sucks Air from Air Filter housing but in CNG vehicles it also sucks CNG from low pressure solenoid valve via venture. Good design and opening of venture has lot to do with idle adjustment screw and screw on low pressure solenoid which members have discussed and explained earlier.
CNG mechanics tends to block Air Filter housing in-order to increase the vacuum pressure in Air Filter housing that?s a bad practice but only advantage it gives is that vacuum sucks more CNG is sucked from low pressure solenoid valve.
Adjustment screws such as on low pressure solenoid valve and idle rpm screw on CNG regulator is very sensitive to design of this venture. Like if venture is a bad design then it your idle rpm will always create problems and no matter how much you try to adjust idle rpm screw, it will have a little affect.
Below are the pictures of bad venture along with a burner type venture which is supposed to be a correct design. Burner type venture helps you avoid blocking CNG housing, it improves the pickup of your vehicle and in return pick of your vehicle also increases. With little adjustment of idle screw you can easily make your car stable on idle RPM.
Widely a common problem in Pakistan as every shop sells a bad venture.