Hello,
 
Not sure how this happened but I need some suggestions on a Honda GX240. Oil is full. It was surging. Instead of rebuilding/cleaning the carb (engine is about 18 years old) I bought an OEM carb from JacksSmallEngine.com. I replaced the carb and the gaskets, replaced the fuel filter, put in an OEM spark plug. I go to start it up and nothing. It’s getting a spark. I tried starter fluid, and nothing. I put a little gas in the cylinder head and nothing. I put the old carb back on and it will not start. What the heck is going on with it. I cannot figure it out.

Check for spark by grounding the plug to the head and observing for spark. 
Even of you get spark, try another known good plug. 
 
Pull the fuel line to the carb and see if fuel actually flows.  There's usually a fuel filter inside the tank.
if clogged / semi clogged, will cause no start and/or surging..
 
.

Sorry I should have mentioned it has a spark, and the a new fuel line with fuel reaching the bowl on the carb, and I changed the fuel filter

Check valve clearances and compression.  
 
Sometimes adding a couple teaspoons of engine oil thru the spark plug hole.
This will help with compression (and sucking fuel / air) into the cylinder. 
(I'll do this on a non starting engine with maybe 50/50 percent it working)
 
.