Don't use ether if
you cant get proper start RPM
and don't know the engine...it will work against you.
It is very probable you need your starter rebuilt as well if it sounds like its dragging or as you say needs hot batteries...Starter Probably needed done a long time ago and the PO never did it.
Always start with the simple things first...
1) Clean all cable terminals and posts making sure of good tight contact ( this means taking each of them off ) Look at each cable end closely ..if the bare wires disappearing into the cable lug are all green with corrosion
..you probably need new ones..as they are giving to much internal resistance to current
and the starter isnt getting full amperage from the battery
...Again check EVERY cable..follow the flow of current
from the battery
..through your switch to the clinoid to the starter..everything!..then do the same with the ground leg.
2) Replace or fully charge and load test existing battery.
or replace starer if engine easily turn over by hand and the above checks out
She will fire with enough RPM
and clean air free fuel
to the injectors.
Have some patients and go down the list..It will be something simple I can all but guarantee you of that.
Iv done it many times...
You should be able to get plenty of RPM from a good starter and battrie to start her after 50 or so revolutions by hand.