The reeds should seat flat, and using starting fluid can
be hard on the reeds, wash away the cylinder lubricant, etc.
I prefer to use fogging oil in a spray can.

No reed valves seal perfectly…  I really kinda doubt they are to blame.  The engine fires briefly on staring fluid, so that says to me there is a fuel supply/delivery issue.  Have you had the carb apart?  Perhaps the float needle is stuck closed.

Try this:

Connect the fuel line and pump it up.  Now, loosen the high speed needle packing nut and remove the needle from the carb?  Fuel should come dribbling out.  If not, fuel isn’t making it up to the carb, or the inlet needle is stuck.  Try pulling the fuel line off the carb, then pumping the fuel bulb.  Fuel should come pouring out of the disconnected fuel line.

If fuel flows out of the fuel line, then it is a carb issue.

If no fuel flows from the fuel line while pumping the bulb, then you have some sort of delivery issue, probably  the tank/line/connector.

for fuel to be sucked in the crankcase  from the carb it must have  sufficient vacum during the uptroke  of the pistons .  if anything is causiing a vacum leak other than via the carb

fuel pull  in will be limited.

Test it by  putting your hand on the carb face  while a friend pulls the starter rope.   you should feel the vacum.

have you pulled the dime size plug on top off the carb to clean out the 3 small drip holes  of the LS circuit. ???   the side channel leading to the top of the carb is very  narrow.

see diagrams of a different carb.. and your’s .            Small carb’s side channel works the same  way. 

make certain the  side channel is 100% and  carb cleaner makes it to the top chamber. . with  the LS needle out  carb cleaner should exit the  needle passage also when injected in the side  channel

if you  plug the needle  threaded openning with a finger   carb cleaner should  exit freely in the drip chamber.

replace and seal the top plug rim  with  finger nail polish  (any color works 🙂  )

make certain you have the proper carb gasket and the side  channel is not obstructed  stopping fuel flow up to the drip chamber.

OK, so you had the carburetor apart a few times.  You mentioned using some sort of sealer on those intake gaskets, which may cause an issue, those gaskets should be installed “dry”.  The two intake gaskets are different, and can not be mixed up.  There will be an internal air leak if the gasket meant for the front of the reed plate is used on the back (crankcase side).  So, you may want to order two new gaskets (remember they have different part numbers), clean the reed plate of all sealer, and replace those gaskets.

So, you are saying that gas/oil is getting into the carburetor bowl, but the carb doesn’t seem to be able to deliver it to the engine.  Perhaps you don’t have the needle valves set to their proper positions.

The high speed needle (lower one), should be backed out 3/4 turn after being gently seated.  The low speed needle (upper one) should be backed out about 1.5 turns after being gently seated.   You mentioned replacing the float, did you replace the inlet needle/seat as well?  Sometimes those inlet needles get stuck and don’t open properly.  Did you use OEM carb parts, or aftermarket?  Oftentimes that aftermarket stuff doesn’t fit properly jamming the float so it doesn’t move freely inside the carburetor.  Once again, you have confirmed that fuel is flowing into the carburetor bowl??