Has a manga series ever affected Jump or similar magazines sales a lot?
I've found you an article that show some graphs about Jump sales, and data about their best selling mangas that I think you'll find useful :

source

And some date from best selling mangas to help you evaluate those graphs : 

Saint Seiya (1986 - 1990) 

Dragon Quest: Dai no Daibouken (1989 - 1996) 

Hokuto no Ken (1983 - 1988) 

Slam Dunk (1990 - 1996) 

YuYu Hakusho (1990 - 1994)