Make sure the primer line is connected good at both ends, and isn't pinched anywhere. On the left hand side of the carb there's a small decal with some numbers on it. Behind that decal, there's an adjuster for what I believe is the air/fuel ratio. With the mower running, you may need to make an adjustment there, especially if it surges any.
Also, since
there's no fuel shut-off on the later Lawn-Boys, after sitting a long period of time, fuel will seep past the needle & seat, and find its way into the crankcase. There's a small plate with 4 bolts under the deck you have to remove to get to the exhaust port, and the u-shaped tube. If you cleaned that area, did raw fuel pour out of there when you took the plate off? Another sign of that on most Duraforces is the stain on the front of the deck where that unused fuel gets spit out of the muffler. Having all that said, go buy an in-line fuel shut-off, and a new needle & seat kit. I recommend eBay for the carb part. Good luck. Hope I was of some help