Gilera runner 50 2002 wont start. Please help

[one333]

Hi, I have one big problem and would like to ask for help if anyone has any idea for solution. And sorry for any spelling mistakes cause english is my second language...

The scooter wont start anymore. After a 50km trip I couldn't get it to start anymore. At home later I checked compression and it was only 2.5 atmosphere, so I thought the piston might got burned or something. So I bought new one but it didn't fix compression. So I bought new cylinder+piston+head for 60€ on german ebay and instal everything. Compression is still 2 atmosphere, I don't know why? Maybe it is because its totaly new cylinder and it needs some use?

I am trying to start it on electric start, I checked that spark plug is working and I even try to pour a bit of gasoline into cylinder for a start kick. I can hear piston banging but it won't start.

Picture of newly instales cylinder:
https://s1.postimg.org/kcnfcifkb/2015_04_17_17_47_50.jpg

Any ideas?
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