I just installed a set of Hard Krome slash cut slip-ons on my 93 Virago. It starts as easy as ever and runs stronger at low end and top end. The midrange appears a little weaker. I have what appears to me as excessive backfire every time I deaccellerate. Is this normal? After running well over 300 miles my pipes are still showing very little black at the exhaust ends. Am I running too lean? If so would enriching the mixture help the backfire problem? FK