I recently acquired this bike and it has several minor issues but the major one is the fuel filter. The previous owner did some sort of rebuild and it does indeed run like a dream until you put on the fuel filter. Taking its top speed down from around 32 MPH to barely 20 MPH, don't even mention hills. That practically kills the engine.
I'm assuming it's a fuel mixture issue, but I'm not entirely sure how to go about adjusting it, however, I do have a shop manual.