There's several specialist forums that'd be a better place to ask, as they offer specialist and enthusiast support. Here's a couple. More out there.
https://itistheride.boards.net/thread/2097/loss-50cc-scooter-slow
https://www.scootershack.co.uk/threads/removed-washer-but-speed-decrease.30555/
Ddhf
October 2022
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