Backfire how tailpipe or intake.Tail pipe could be timimg,So could intake.Intake could also be a lean condition.Plugs have also been known to cause this.A good tune up will help if you can find one to trade on.If someone thinks its broke then they will want more boot.Outside lifts tend to bring more as they can be used inside or out solid tire lifts tend to only wat to run on hard a surface.