Dani,


Although the engine is mounted a little low, in relation to the fuel tank (the middle of the carburettor barrel should be at the same height as the tank's center-line), it should have no problems running as it is in a trainer.

The problem I see immediately is the fuel line, which is about 10 cm too long.
Cut the excess, so it will just reach the fuel nipple...

Also, has the nozzle been loosened? The nipple must be nearly horizontal.

Once the engine has accumulated a few hours of running time, it should be dead reliable; not dead-sticking.