1982 GPZ 550 Backfiring and poping

I have flooded the engine due to the faulty petcock. I have tried to start the engine but it would not crank because the cylinder was full of fuel.
Fuel got in oil as well. Changed the oil and a filter, removed spark plugs and cleared cylinders from fuel.
Now it starts ok but pops in the engine and trough the exhaust. I have noticed it occurs when I close the choke.
What happened? Before flooding it ran well. I hope I did not damage the valves or something.

I don't know the answer, but it is not only the petcock that was faulty. The carbs also have a problem or they would have prevented the fuel from flowing after the carbs were full. I would be sure to correct the carb problem or you may experience a repeat. Ed

Like Ed said, you still have carb problems if it flooded like that.

You will have to make sure the float valves can seal off the fuel flow and that the fuel level (float level) is set correctly. The manual explains how to do that.

Float valve on 1 cylinder carb is leaky. I am aware of that for some time now. Clear hose test showed me that.
Aldough, It took for 1 week to fill the cylinder with fuel up to the point of hydrolocking. Took out the spark plug and it vas BLACK as cole. So, no cumbustion!
What I beleive has happened is that, the excess fuel in cylinder carbonised the spark plug.
That cylinder misfired due to weak/none spark and that caused the popping, puffing and backfireing.
Cleaning the spark plugs solved the problem. No more popping, puffing and backfireing and the engine runs great at any regime (idle, midrange, high rev).
Nevertheless, carbs must go down and the first one, the leaky one, needs my attention.