Sitting that long it sounds like jets are clogged, causing it to not pull fuel up from the bowl.
Please dont take this the wrong way, as I dont know your skill set.
Did you take the carbs completely apart, soak em in a good carb cleaner and blow compressed air and brake cleaner thru every little hole and orifice?
You said you rebuilt the fuel pump?
Is it possible a gasket or checkvalve didnt go on right?
For what its worth, a new complete fuel pump costs less than the rebuild kit (dont ask me why)
^This, I say it all the time I don't rebuild fuel pumps I buy new ones.
I didn't read every post, but your engine is as simple as it comes.
1 Check Comp.
2 Check spark
3 Fuel
If one is bad find a new engine, if 2 is bad let me or Cut know and we will walk you through it, If 1 & 2 are good then its #3.
How to check spark with out a spark tester, remove both spark plugs from the Cyc. put the plug in the coil wire hold it tight to the block for ground and pull the pull cable the spark will jump the gap and you should be able to see. Repeat for the bottom cyc.
If the plug is not grounded it will give you a little shock but it won't hurt you!!!
*DO NOT DO THIS ON ANY OTHER MOTOR UNLESS YOUR SURE OF THE VOLTAGE, SOME NEWER ENGINES WILL SEND YOUR BUTT TO THE HOSPITAL*
Once you have checked the 1st 2 things, will you be able to diag your engine properly. Until then your guessing!