tohatsu 8hp won't run but a few seconds

I have a 2014 Tohatsu 8hp with very low miles. My brother put fuel in the crankcase! I know I know! So I drained that, put the correct oil in, took the carbeurator down, soaked it in cleaner, replaced the bowl gasket. Nothing looked damaged. New plugs. Reassembled it all hooked up fuel lines. The bulb will not get hard, yet I cannot find anywhere fuel is leaking. I can hear the gas coming into the carb when I squeeze. I tried starting it, it will start, but only runs a few seconds and then only with choke fully open. Then it will just die. The first time I tried it, it backfired, but not subsequent times. It just runs a few seconds and dies. IT is not running rough, it just runs then dies. What could be the problem?

Sounds like it's too lean. Especially if it needs choke to run. Did you mean fully choked, or choke fully off? Either need to do a more thorough carb cleaning, or the float/needle/seat may be wrong.
The primer should firm up. If not, the check valves in the bulb may be leaking. Otherwise, one would expect to see fuel dripping if the needle did not seat properly.