Kawasaki he5 no longer starts “right”

Hello, I bought a Kawasaki ER-500A a short time ago. BJ97 – ~50,000km. today I drove about 20km without any problems. I left my bike about 1/2h. After that I wanted to start it again, but unfortunately you could only hear a funny “KLACK-KLACK” while pressing on the starter. You can only put the “first” and the “empty run” in, all the other gears are blocked. They are hard to set up while it is being pushed. A nice man helped me with the attack. After the second attempt with the 3rd course she started again. The engine turned up constantly in the stand, but I could drive up to home. At home I put it off, waited for a moment and started it again with the E-starter. As if never had been anything, she started immediately again. About 1h later I went back to my motorcycle. Suddenly I saw a cymbal-sized gasoline leak on the ground and it continued to drip off the carburetor. I wanted to run it right away. and then again the same as before: It only did KLACK KLACK!! A friend of mine then helped me to run. However, without success. Each gear blocks the rear wheel. I hope you can help me. Thank you )