Had spark but dirty black plug, finally it did not want to run at all.
If you have a petrol inline valve using the vacuum. Disconnect the vacuum hose and close it of with a screw to prevent air flowing into your inlet. If you not use that hose anyway make sure that false air never can enter at where it is on your inlet.
Put your petrol gauge at "PRImer". Then it has free flow. The other ways it should be closed.
Start and go.
If this was the problem, then diafragms in the petrol valve are leaking and sucks more or less illigal petrol through the hose that makes running terribel, or not at all.
