I think the actual reason of this is the fact that Euro II systems are designed to be installed on a Fuel Injected engine, where the injectors only supply fuel at the intake cycle, unlike the carburetor which mixes the air+fuel beforehand and so there is fuel in the line when the combustion cleanup if on way, there was some regulation of some international laws due to which all car manufacturers had to upgrade to at least Euro II by 2012, even in Pakistan,,, thats why they changed Mehran to Euro II, and thank God they didn't just put a EGR (Exhaust Gas Recalculation) valve on Carby Mehran, and did it the proper way, but our Bike industry is still Rocking the 35 year old CB 125 Engines, and so they decided to easily get away by putting a easy cheap solution to it, i am amazed they didn't just put a Sticker of EuroII, and actually tried something,