I bought a brand new Briggs Intek twin 656cc 20hp. Swapped it onto my 1987 John Deere SX95 rear engine. Finally cranked it up today, and it runs rough and has no power. If I unplug one cylinder it makes no difference whatsoever. Swapped the spark plugs from one cylinder the the other and no difference. I guess I'll do a compression test tomorrow and go from there. Anyone have this problem before? Hopefully I'm overlooking something simple. Thanks