It used to be legal in Hawaii, until around 2003 when the law was erased--something to do with local politics, bribery, and Segway machines.
The Hawaii laws currently don't define motorized bikes, but a bill to replace the law is in the works for next year. Unfortunately, the new law will only define electric motorized bikes and not internal combustion engines.
I think the laws on motorized bikes are also undefined in New York, and I'm not sure of Pennsylvania.