I have had problems starting my Valp. Once starting it is running well.

Have changed petrol pump, checked the ignition point, opened the carburettor to clean it, but still I have problems starting the engine.

I have the standard Zenit carburettor, however when I bought the car the spark plugs had been changed to normal sparkplugs (Not shielded military type). In addition the distributor cap and wiring between the distributor and the spark plugs.

Would appresiate any hints on where to start looking for the cause of this problem.

Thank you in advance :-)

Is your valp difficult to start every time or just when it has stand still for awhile?
Have you had this car for long?

I have had the car for four years now, and it has been relatively easy to start. Now I am experiencing that it becomes hard to start when the engine is luke warm. Not a problem to start it when it is cold nor when it is warm. This weekend I opened up the carburettor and cleaned it. However the result was the same.
I have checked the sparks on all plugs and they seem to be working well. I have checked the ignition timing an that is according to the description.

Thank you in advance for your advise.

Sounds like you have a problem with the cables between the distributor cap and the spark plugs (and/or the one going to the coil). If you have a sivile, 12 volts system, I would recommend that you change all 5 cables.