As said, if the 4.5 electric was right you need at least a 9 HP to run it. I ran a bigger Alamo on a 6.5 Honda but could only get 17" vacuum because even with the weight of the engine on it the 2 belts slipped and then burned the belts anytime it started to climb over 17". That had a 2.75" double pulley on the engine. When I had a 3" drive pulley it lugged the engine down. I suggest 9 HP or more and at least a 3.5" drive double pulley or regulate it down to 17" max with a 2.75".
Dave Klish, I recently ordered a 2x6 wood fired evaporator from A&A Sheet Metal which I will be converting to oil fired
Now have solar, 2x6 finish pan, 5 bank 7x7 filter press, large water jacketed bottler, and tankless water heater.
Recently bought another Gingerich RO, this one was a 125, but a second membrane was added thus is a 250, like I had.
After running a 2x3, a 2x6, 3x8 tapping from 79 taps up to 1320 all woodfired, now I'm going to a 2x6 oil fired and a 200-425 taps.