1 cylinder down

[john leonard]

1996, 24K miles - Advice needed
My 3-year old replacement petcock malfunctioned and loaded carburetor #3 with fuel about a month ago, preventing the bike from starting.  What I did:
- rebuilt and tested the petcock- drained the fuel and oil- removed the air filter- removed the plugs and tested their spark on the engine case- with the plugs out, I cranked it over until the chamber was clear- put it all back together and started the bike and ran it for about 15 minutes
But now, I think it's running on 3 cylinders. (no backfiring)** Last fall it ran like this too one day, but corrected itself after about 10 minutes of riding. **
The top end sounds fine - I don't think I bent any values when it locked.
I'm assuming that the carburetor that flooded has a bad float - at least. 
Q: Can a stuck open float cause the cylinder to not fire?
Q: If I open the carburetor to inspect it, would I need a new gasket kit or do they typically stay intact when opened?
Q: What's next?
Thanks in advance!
john