If you have an aftermarket exhaust you need the proper jets to match.
Stock bikes from the factory are setup to get the best possible mileage and lowest emissions. If you change the intake air cleaner, the exhaust, the cams, pistons... then you have changed the jet size required for the proper fuel ratio
An engine will tolerate running a bit rich, but running lean raises the temperature in the cylinders and the heads.
EDIT ADDED: if you essentially have straight pipes with no baffles, you should be able to find a table with the right jet size to use, even though you dont know who made the exhaust.
Last edited by KCW; 05-04-2018 at 11:51 AM.