Suzuki GSF 600 Bandit cylinder 4 defective

Hello, My Bandit has a more complicated problem with the cylinder No. 4. It started like this: after service life the bike failed after about 2 km. I discovered a lot of petrol in the air filter box and the engine blocked (though on the 4th cylinder). Petrol was then also in the engine oil. I then changed the petrol tap and opened the corresponding carburettor, discovered dirt on the float needle valve, removed and replaced the valve. The blocking of the engine was with the disassembly d The engine still doesn’t run. I checked the spark plugs and coils. After changing the two ignition coils, the engine ran briefly on all 4 but only briefly. Out of the question is again cylinder 4 and not as hoped another (as coils replaced). I’m at a loss. I don’t know what else it can be, except for a defective engine. (40tkm of barrel) is not too much) Does anyone have experience with such a problem here? Many thanks and greetings, Lenny