Q. Why 4v fi more costly, what's different about 4v and 4v fi?

EFI is a version which consists of ece boards and sensors which sense the amount of petrol to be sent to the engine depending on the power. Where as in carb version it is fully mechanical as in old bikes. The major difference is the EFI versions gives some point difference in mileage. I prefer the carb because it has only some minor difference.

The number of sensors used in engines is different....sensors ensures the proper utilisation of every Last drop of fuel...thats why fi engine provides more milage

Fi shows which gear you are in..has ECU which is required for Fi..and hence is costly.. moreover it has more power over the carb