Do you use the choke properly? User manual has often errors in that matter.
Before you try to start the warm engine, set the chocke lever in opposite position. Maybe the choke is "permanently ON".
This is my first thought to your problem.

How is it with fuel consumption?

The secound though is, maybe you should set the valve clearence. It could cause simmiraly problems.

Btw. under which make is sold the Zongshen in Croatia? In Poland it is sold as Junak 131.