I have the URL of the complete installation and care instructions for the lawn sweeper at:managemylife.com/mmh/lis_pdf/OWNM/L0708269.pdf
In addition to numerous bolts and nuts being required to first set up the sweeper, there is the need to periodically go through the unit with a wrench, to make sure none of the tubing supports have loosened.
The words clean, oil and grease appear multiple times with this machine.
And, there is an internal chain drive system located internally, on both wheels of the sweeper.
If the machine is being run "dry" or has been a while since last lubricated, your difficulties could be coming from the machine having to try to overcome too much internal friction.
Oil is good.