Backfire When I Shift

[MustangMatt1966]

Hey guys, just a quick question. When i am running through the gears (usually when I am on the gas a bit haha ) every time I shift it backfires, just one loud pop. Car seems to be running fine and the backfire sounds kind of cool but I need to know what is causing it. Thanks guys

 

[302 coupe]

too rich, incorrect igntion timing, or somehow the exhaust valve is staying open too late.

 

[Dark Knight]

Or an exhaust leak in the system somewhere.

 

[MustangMatt1966]

Or an exhaust leak in the system somewhere.

I was thinking exhaust leak, replaced both header gaskets, one was blown and then double gasket'ed the collectors...should not have any leaks...but i do feel i need to tune it, it may be rich....dont think the timing is off though..