It is probably a lean seizure due to lack of fuel. Fix the cap before riding further. Sooner or later you'll kill it.
In reality there's no such thing as a partial seizure. If it sticks and stops running it's a seizure. There are varying degrees of damage from seizure. Pull the pipe and have a peek into the exhaust port to see the damage. Post up some photos if ya can.
you don't see luggage racks on a hearse..........act accordingly