well.. gas dripping out the exhaust port? There might be a clue.
All the symptoms..slow acceleration and low top speed and hard starting could all point to a carburation problem.
The question is what did you do lately that may have caused the sudden change? Did this start since you refilled the tank or since something on the bike was repaired? Hopefully you might remember something.. That would narrow down the search.
Otherwise it seems that the engine is running very rich. If you did absolutely nothing fuel-related then perhaps something broke or went out of adjustment. Something like running with the choke partially closed might do this.
Take an hour or two off and go over everything .. check all cable adjustments, bolt tightness and all the other routine checks, especially as are related to the carburetor.