`82 Yamaha XJ650 Won't Start But Runs Great NEED ADVICE

I have a 1982 Yamaha XJ650 Maxim with about 11K miles on it.

The problem is that it is very hard to start or won't start - unless I put a
very small amount of starter fluid in the air box opening. Once I do this,
it starts right up and runs well. Idles a little slow until warm (I think
this is normal). After 2-3 minutes, idles and runs great. Once the bike is
warm, it will start again with no problem at all. I have tried starting it
with the choke in various positions. With the choke on full, it will
sometimes sputter for 1-2 seconds, and then die. Then it seems like once it
has done this "sputter" thing, it won't even fire until I let it sit for
about 15-20 minutes. One 1 second shot of starter fluid seems to fix the
problem completely.

Here is what I have tried so far:

Cleaned carbs. (twice, very thoroughly, a big pain)
Replaced the jets in the carbs (main and pilot, the second time I cleaned
the carbs)
Replaced fuel line
Used a gas tank restoration kit (insideof tank did have a little rust)
Added an inline fuel filter (works the same with or without the inline
filter installed)
Replaced air filter
Inspected intake boots carefully for leaks.
Tested the vacuum activated fuel petcock

Obviously it is not getting enough fuel to start, but I am baffled why such
a small amount of starter fluid seems to completely fix the problem.

I have not synchronized the carbs. The previous owner said they had just
been sync'ed. Since it idles fine once warm, I don't this this would be the
problem, but I am not sure.

I would appreciate any advice.