Michael, it's the main handles/levers, there are two on the ' hub' which have to be pushed to the right to engage the down feed. Any vibration when using power down feed will cause them to'jump out of gear' and the quill flies back up!
i just had a look at the Chester lux and if yours is the same it has three handles on the main down feed. My machine is circa 2008 and it looks like on the warco machines that the down feed has been changed to the 3 handle version like yours.
i would be interested to know how you engage fine down feed
Deic