I have an MV Agusta Brutale 675 with a GPR Carbonox slip on installed. The air filter is stock and no work has been done on the ECU. My problem is: at this state it's running rich as one can smell un burnt gasoline in the exhasut fumes. It's also got poor mileage as well. I'm thinking about installing an aftermarket air filter i.e DNA, BMC, etc which would hopefully remedy this, however plan on doing so without installing an aftermarket feul controller (i.e Power Commander, Bazzazz). Will this fix my problem or worsen it?
If anything, your bike should be running lean
You put an aftermarket non-restrictive exhaust on your MV, that increases the flow of gasses which requires more fuel to compensate for the additional flow. So, the idea that your bike is running rich doesn't really resonate. It certainly can be and if it is it could be indicative of another issue within your fuel delivery system.
A free flow air filter will give you a higher flow rate through your intake than an OEM filter typically. This will add the ability for your engine to consume more gasses, in this case, air. Which in theory would reduce richness, but wait....there's more.
You have an ECU, it monitors your intake and exhaust. It should be providing the correct richness without a Power Commander. Why would it be rich? It shouldn't be rich. It should be leaner.
You have something else wrong with your system. You should clean all your sensors. MAF, oxygen....all of them. Once they have been cleaned, go for a ride and get everything good and hot and then see if it still smells rich.
The K&N and Power Commander are great low cost HP upgrades but I believe you need to understand what is happening with your bike in it's current state, fix it, then add those pieces in. Your bike should not be running rich or lean, it should have perfect AFR and there is a reason it doesn't. You just need to find it. Also, clean your plugs and check your wires and ensure you don't have a misfire.