1) The machine was running low on oil
2) The machine was running to fast without enough time for the wicks to fill back up properly like J.V. stated
3) To thick of an oil was used and would not feed onto the wicks.
4) The batch of oil was bad (don't think for a minute that this doesn't happen)
5) The brushes are woren or starting to wear out.
6) To much stripper being used
7) Faulty filler line feeding tray to wicks.
Pump is beginning to fail
9) Contacts that apply wicks to belts are shorting (would be noisy)
10)Poor machine maintaince
That oughta get you going.
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EvEryOnE rOlls OvEr thE lanE bEd