I have a Bolens with a Briggs+Stratton - Intek V Twin OHV 20 hp. It's been running very rough some times almost sounds like its going to stall. I can find a sweet spot if I pull the choke out 1/4 to 1/2 and have the throttle lever up about 3/4 of the way to make it run smoother but not 100%. I put new spark plugs and a new fuel filter but still runs the same. Would you think the carb needs adjusted or rebuilt or do you think it might be something else? Thanks