Re: what did you do to your motor bike today?
KDB, I had the same problem when I ran mine without a tensioner. Are you using the rag joint? Do you get a lot of vibration? Getting the chain extra tight is NOT the answer. The tighter you get it, the more it will stretch anyway, and the faster that motor will "walk" that axle forward, no matter how you crank on it. Then you will have to rebuild your hub components on a new axle when you strip out the threads.
Check my User Page for a spring dampener roller, or ask around for spring tensioners and chainstay-to-seat stay flat bars that use the roller wheel (can't turn into the spokes)
The heavier chain you can go with, the better!
1" roller Dax Friction Drive and Tanaka 3300 with mods.