Question about throttle controls on Hyster H40XL diesel forklift

Hello Everyone,

I just picked up a 1989 Hyster H40XL-MIL diesel forklift. It's a hydrostatic lift with a shuttle shift on the column. The peddle controls the speed of the engine as well as engaging the transmission. There is also a knob marked, STOP, RUN, ENRICH. It's like a choke knob and once the engine is running, the only way to stop it is to pull it all the way out. It appears to control the fuel delivery on the injection pump and the peddle looks to control air flow in to the intake. Seems backwards to me but it works.

At any rate, my question is what does the choke looking knob do? If I push it all the way in I blow a lot of black smoke on a heavy peddle. If I pull it out a little to what would be considered the RUN position it seems to burn cleaner. All the way out obviously stalls the engine. What's the purpose of the extra fuel setting? When would I need it? I've been leaving it in what would be considered the RUN position. Just wondering if there's a better way I should be using this control?

Thanks,
Scott