if you have thick dark build up on the spark plug than that can mean either your running rich or you have alot of carbon build up in the block.

Also, how would you fix a running rich problem? I am running really rich on my 95 gsr in my 92 civic. It runs well, but is running very rich and has lots of backfire(including flames). I have contemplated to just get an adjustable fuel pressure regulator, but is there a cheaper solution?