Here's a common cause of the ongoing belt slipping issue.
The vibrations of the machine during use causes the adjustment screws to back-out. That's why the belt never stays adjusted, thus a continuous cycle of frustrating re-adjustments.
The fix (as it worked for me. Where I was once adjusting every 3 miles, since this action I haven't adjusted in over 50 miles.):
Thread Locker
Home Depot sells two types of Loctite Thread Locker; a permanent lock and a temporary lock
The temporary lock, red tube, blue contents, locks the screw in place. This is made for such an application, where vibrations cause screws to unwind.
When you eventually need to re-adjust, use your wrench to unlock, reapply, readjust, then run.
Peace
The Bos
The Bos
September 2010