Hi I have an 06 FXSTI that I bought used.The first owner put screaming eagles on it. He also put on a high performance HD air filter. Now the back of my breather box has been taken off. The bike runs great when I am going down the highway, but when I back off the throttle to slow down it will spit and backfire. It also does not like to go slow. It run ruff if I have to ride from idle to about 25 mph. Is there anything that I can do to get it to run better. That will not break the bank? Maybe go back to the stock air filter. Thanks in advance!