[Piaggio Zip 2 4T] Start problems with rain / humidity

Hello dear people, I have just solved a problem with my light, there is already a new one. And this time it is perhaps even worse… Actually it is not really a new one, but since it was quite dry and mild in Berlin the last days, I had no problems. The problem course looks like this: a few weeks ago I did a rain ride of about 15 minutes without any problems. Arrived and left the scooter for a few hours (in the rain). When I was He went on to start it again, but spoke only minimally to the gas attack. I.e. even if I turned it up to the maximum, the speed did not go up enough to start it. The relatively strong smell of petrol in the air was also noticeable during all the unsuccessful start attempts. In addition, he did not go on at all after a few start attempts, or only for a second and then again. With a friend I then have the ignition a few days later in dry weather erze developed, cleaned, successfully tested for sparks and reinstalled. And then it ran again. A few days later I had the same problem again in damp weather. This time I simply put on good luck myself and installed a new spark plug from NGK. Unfortunately this had no effect immediately, the scooter did not work. I believe already the next day, it was dry again, I did, without first a start attempt, directly again the new spark plug Since then it has remained dry and, except for the separate problem with the passing beam, I no longer had comparable failures. Now we have arrived today. This morning it did not rain strongly but permanently. I start the scooter successfully and thus drive about a kilometer without any problems. When I want to stop at a traffic light and start driving green, I notice that the scooter again does not have any problems. fs responds to gas. So I push it onto the sidewalk and have described exactly the same symptoms as at the top again. After a first research I am now inclined to simply exchange the spark plug, but what does your experience tell you? What could it be? Be happy about every hint as always. Best regards!