First Layer issue -3D printing

Hi guys,
I got a first layer issue during printing PLA. I have tried several times but still have same problems. At the beginning the print was quite nice, but after a while, these is are "bumps" on the surface. Some people said it is about the distance between nozzle and the bed. I have done some adjustments on the distance but problem still exists.
I'm using the Flashforge Finder, which has a pre-cut blue tape on the build plate and has no heated bed.
It would be grateful if someone can help me to solve this problem. Thanks a lot.



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Please provide more details -

What model are you trying to print?
What slicer are you using?
What settings are you using (temperatures, travel speeds, etc)?
Have you calibrated this material?

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