always wear your helmet. every cop i've talked to always says the same thing, "wear a helmet and don't ride like an idiot and you
should be fine..."
another thing to remember, is you are no longer riding a bicycle, and the things you used to get away with, like rolling through 4-way stops, turning right without stopping, riding on the sidewalk, riding on the wrong side of the street, and bunny hopping trashcans, or whatever, are now even more illegal. (not sure if bunnyhopping trashcans is illegal

)
what i'm saying, is, you're not just a kid on a bike anymore. you're a guy with a half-a$$ed motorcycle, and a lot more noticeable. a cop might let you slide if you're on your bicycle and you coast through a stop sign or something, but you are now riding a motorized vehicle. thinking like a cop for a minute, it's not worth it for me to pull over a kid riding his bicycle against traffic on the sidewalk, but if he's got a motor, i'm gonna teach him a lesson...
by the way, there's a kid down the street that had a motorized bike, he got a ticket for not wearing a helmet, which was doubled because he was under 18, and his mommy made him sell the bike to pay for the ticket. and after he sold the bike, he still owed his mom for the rest. i think he said it was $600. and, he was a block away from home.
so my advice to you, is even if you're just going around the block to test out something, or whatever, WEAR YOUR HELMET!