82 931 fuel lean out around 2500 rpm?

[Jrboulder]

I'm looking at a 931 that's for sale. The seller says it leans way out around 2500 rpm and starts backfiring. I don't think he knows much about CIS and neither do I. I understand the best way to know whats going on is to do a pressure test, but the car isn't that close and I'd like to know if this usually means it's something very serious, or if it's more than likely just something minor.

Thanks!