Reed Engine starting problem
You mentioned that you are using a copper reed & you have repeatedly cleaned it.
Is it possible you damaged it. They are very, very fragile If it is the least bit bent or creased it is no good.
Some people prefer plastic (mylar) reeds as they are more resistant to damage.
In any case here is how I test them.
With the reed installed & the fuel tank removed, place a piece of flexible fuel line over the venturi extension & blow . The reed should let air pass. Now suck on it . The reed must seal the passage. If the reed is not sealing, air will pass. If this is happening, replace reed.
Of course you have previously made sure that the needle valve seat & fuel passage is clean & the venturi hole is clean. Also the short internal fuel line is tight on it's nipple & that it reaches down into the fuel in the tank.
Good luck.
Bob G