Timing lights are cool.
I've noticed that if I pull the choke out the moment before I turn it off he shake is much shorter or doesn't even happen. Usually this is caused by a high idle speed, an over-rich mixture, and lots of carbon deposits. When you pull out the choke control you are making an unburnable mixture which helps to stop the self-ignition. Check that the idle speed is well below 1000 RPM, and that the mixture is adjusted lean. You may find a vacuum leak or two.