Hello guys my Suzuki RG 80 always goes out, who can help?

Hello together, I ask for help, because with my newly bought Suzuki Gamma something is not right. I describe the problem. It starts, however, only with Choke and then turns up to 5000 and goes off. Now I pushed you once without Choke and see as it runs and stays on, however you have to keep the speed always over 3000 revolutions. So far I have done the following: Cylinder and piston down everything resealed (cylinder has a few small bars on the back below and at the inlet side, roughness depth in the hundredth part, where I don’t think this is the cause, because the area is in order with and under the piston rings). The suction nozzle, carburettor and membrane absorption were cleaned and metal membrane replaced by carbon membrane. The air filter is cleaned, the combustible arrow is replaced to the exhaust outlet side and the crusher seal is guaranteed. Can it be that it is an undic on the crankshaft Has anyone ever had the same problem? Please for help don’t know where to continue. Thank you in advance Best regards