If there was any single exhaust i would have to guess would be fitted wrong and be too close to the airbox, that would be the one! The exhaust itself is pretty crappy, in all honesty you're going to lose power over the stock one, but DG isn't exactly known for good fitment either. I bet it's sitting way too close to the airbox.
If the carb isn't jetted right that'll compound the problems, that exhaust is way too free flowing for a stock motor and will require the jetting to be a lot richer than stock as it's offering pretty much zero back pressure.
My suggestion, instead of shielding your airbox, ditch that piece of **** exhaust on ebay and get yourself a stock one, or a better aftermarket one if you like the noise makers.
If the carb isn't jetted right that'll compound the problems, that exhaust is way too free flowing for a stock motor and will require the jetting to be a lot richer than stock as it's offering pretty much zero back pressure.
My suggestion, instead of shielding your airbox, ditch that piece of **** exhaust on ebay and get yourself a stock one, or a better aftermarket one if you like the noise makers.