Need advice on a 1979 JLG 40F boomlift

Hi guys, new here! Just found this forum and thought I"d give it a shot. I'm going to look at a old 1979 JLG 40F boom manlift to purchase. It is private owned by a trucking company who has used it for years to wash and service trailers. They recently bought a newer one and have this one for sale cheap,cheap,cheap. They say everything works fine with no major leaks....except.......it will only start and run if you continue to spray ether. It is a gas engine. He told me his mechanic says it needs a new carburetor but he also told me his mechanic is only a parts changer. Sounds to me like not getting fuel. This happened right after they put in a new battery and hooked it up backwards. They had to replace some kind of relay or something so it would crank but now it wont fire without ether. I plan to see if it is delivering fuel to the carburetor but if it is not, is there some kind of safety fuel shutdown solenoid somewhere that could of also been damaged? What else can I look for that is not necessarily obvious to the average mechanic? Also, what engine is used in these and how much does the whole unit weigh? Thank's

Need advice on a 1979 JLG 40F boomlift