A couple things come to mind
1. Neck bearings
2. The jiffy stand rubber bumper missing or out of adjustment
3. Motor mount bolts loose
4. Some loose or missing front breaks.
5. Not sure if this applies. Are the forks leaking fluid ?
I had the same problem last month and I phyically checked every nut and bolt on the front end. My problem turned out to be sheared motor mount bolts.
Just take your time and good luck finding that problem