I posted last fall that my 500 would not start, and would not even crank over one turn. New starter, solenoid, etc, no matter what battery and booster, still no crank. The last thing I could think of was that the decompression cam (on the exhaust cam) was not doing its job. The starter would only rotate the engine one turn and stop on the compression stroke. So I opened it up and pulled both cams, which were appreciably worn. I ordered new ones and received them a couple of months later. They have been sitting for several months, but I finally got around to the installation and reassembled the engine. I really was not very optimistic about the cure because there didn't seem to be enough wrong with the cams to keep it from starting, and the decompression device seemed rotate the way it's supposed to. To my surprise it cranked over fine, and after several tries fired up! Still need to reassemble body panels and such before a real road test, but I'm chuffed for the moment.