Sounds like the condenser is bad. This will cause the points to arc and the spark plug to fire inconsistently (sputter). The bike will feel like it wants to really go but has slow acceleration. DO NOT BUY THE REPLACEMENT FROM HANDY BIKES, Ive tried one from them in your same year bike and had the same problem. If you can pull it from your parts bike do so, if not try to find a novi one. hope this helps.