Motor failure in Daewo Lanos

I have said now a problem with a Daewo Lanos de Gasolina 1.4
When I started in cold everything normal but after a couple of minutes the engine begins to fail as if it stays in three or two cylinders, the engine then rates and does not break well, loses power.
I have changed the spark plugs, the cables and the ignition module. But it remains the same.
Thanks anticipated

Hello good it may be that it does not injade the gasoline well and that's why you seem that you run out of power

Thanks for the Respuiesta, but I already solved it.
It was about cleaning the hydraulic pushers of the valves, then they ran out of oil and did not comply with their mission.