Thanks w8ye and MercerAUST for answering
I have mounted a seperate fill line with a filling valve of the same reason: To prevent false air to sneek into the feeding line.
Also I have removed the filter last time I changed the tubes and the clunk in the tank.

The 'plug' solution is worth trying - and mybe I should turn the idleneedle 1/4 to a richer mix. One thing at a time?
But how are the carburettors on bigger gas engines fed? is'nt it with separate electric pumps?

Regards Peter