I know no body is going to say "Take that engine off, or else". But you may get told not to ride it. I have been seen by several officers while riding around, none have stopped me. I did not get mine registered. The D.M.V. sucks here in LA. Got to stand in line to be told to stand in another line, and after the 3rd and 4th line ,you find yourself back in the first line. Illegal to own, NO, To ride, frowned upon, Yes. I don't have a problem getting kits, I have family and friends in AZ & UT, just have to pay shipping twice. The law in CA on motorized bicycles / mopeds requires you have head & tail lamps, turn signals, be 50cc or less, not exceed 30mph. So mine WAS NOT legal. No lamps, (did not ride at night) 66cc, X-chamber, top speed of 38mph. I say "was" because it was stole 4 weeks ago. 3rd one in 3 years. Building bikes for other people (thieves) for free is getting old!