Sounds like tthe same problem I was having on a friends stock 50. I must have torn the carb apart 8 times trying to see what was going on.
I finally disconnected the electric choke and problem solved. I disconnected it at the connector.
Try that and see if it works if not I would be curious to know if you are able to get it fixed and what you found.
Hope this helps.
Fischer Mod 90----Nick
2006 WORCS National Champion 51-70 Mod
Extreme Typhoon 125--------Kenzie
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