Nikos,

As delivered from the factory, the fuel line between the regulator and the carburettor on DZ's runs very close to the cylinder head. On very hot days, especially after the engine has been run, this can cause the fuel to partially vapourise in the line. It is good practice to space the line out slightly from the cylinder head or to enclose it in a short length of insulating material.

As for your oil leaks, there could be a number of sources. It is not unusual for some DZ's to come from the factory with bolts that are not fully tightened. Before installing a new engine in an aeroplane, it is worth setting it up on a test bench. Don't run it for longer than is necessary - just long enough to ensure that the idle is steady and that the engine is running up smoothly and reliably to full revs. Before the engine has fully cooled down, check all the bolts to ensure that they are tight. Your leak may be caused by one or more of the 5 cyliner head bolts that is slightly loose or by a loose bolt in the backplate assembly. "O" rings are the other thing to check, though if the engine is new they should be OK unless they have been nipped during assembly.

Best of luck

Bob

PS:
I am assuming that the seal between your manifold and your exhaust is in good shape!