well you do have an ancient piece of equipment there, you'll be very lucky if you find anyone that has any information on that thing :o)
From your description it would either have a continental F162 engine or possibly a Waukesha FC260A and FL260A. There should be a tag on the side of the engine or a stamp.
In either case the LP system would have most likely been the same on either engine.
From your description it sounds like it is starving for fuel or possibly getting too much fuel, the latter indication you would smell rich fuel around the engine if this is the case.

First thing i would do is run a compression test on the cylinders.
If compression is suitable then i would then turn to the adjustments on the mixer.
There should be 2 adjustments on the mixer for coarse fuel intake and also Air mixing.
Are there any markings on the mixer? a mfg name or a model number or something?
Like century or impco? Model 50? 100?