We have a Dempster red pump with 5073 raised numbers on it and Beatrice, Nebraska with a motor - how do you prime this pump?

The replacement oil pump could be defective or installed incorrectly.

prime the pump first

If your motor has come on while the pump house was flooded your motor is probally burnt out and will need to be replaced. when you do this you may want to replumb your pump to raise it above the high water line so this does not happen again. When you do this install a check valve on your suction so you don't have primeing problems later. Good luck

We had the same problem. After dissassembling the whole machine we could not find a clog or any other obvious problem. The manual suggests priming the pump by putting the solution reservoir in and out a few times. This did not help much. What did work was to raise the unit up a few feet above the trigger while depressing the holding the spray trigger. (That is, use gravity to fill the tube.) After solution was flowing freely, we turned the machine on and it seems to spray fine again.
Hope this helps

This is a fairly major job that involves dropping the oil pan from the motor to even get to it.
Depending on motor size, is how difficult it is to get to.
You can do it while the engine is in the car, but it is easier if you pull the motor.

How good are your mechanical abilities? And do you have a good work area to do this in?
Along with, a fairly complete tool set.

But that's the gist of it. Drain the fluids, remove the oil pan, loosen and raise the distributor, pull off the oil pump, clean as needed, put in the new one, replace the seals and gaskets, reinstall the oil pan, prime the pump by running a shaft down the distributor shaft passage, reinstall the distributor, time as needed.
Figure an easy 8 to 10 hours minimum.
As stated, that is the general picture, there are a number of other smaller detail steps.