Hey Kumara,
I am bit new to this forum. I have a Nissan March K10. It is also a carb and it does a pritty good milage. But if you mess with it, it will screw you for good. Yes I agree with carboy coz if you wanna have a good milage it not only the carb you hv to concern on may more things in the car. Even these are not related directly with the carb. Can you be more specific with your car. May be a pic. will try to help you out.