comments:
Sounds like the engine is 4 stroking at wide open throttle / WOT which is fairly typical with a stock #70 main jet. The engine will run rough when 4 stroking due to an excessively rich fuel/air mixture. You can research 4 stroking or post a video so we can hear what it sounds like. This is the best jet selection I am able to find for that carb. https://hybridpowerbikes.com/products/bofeng-carb-jet-set?srsltid=AfmBOorB9Vk5684GliqNeSZMtdUoqTzZee4_iBxwv5BNJgC8VB3oBwen Another option but doesn't include a 62 & 68 jets that allow you to finer tune. https://www.amazon.com/Carburetor-212cc-Jet-Kit-Predator/dp/B0G2SXR424/ref=mp_s_a_1_15?dib=eyJ2IjoiMSJ9.Chy_PGbJpj48u7Z2uLqxxHqKfCSMV0Hev7gxpOjxTw2rEtkPd8-q1bFFa4tA99LFgXoofWoDMF5nQMKLCyfYTONrbyI01XBeyeNuuzp1S4_Q6K5-GDN02HBz7sLObm5bCoTAvcdsGumv8zZ1KEZtAxk4ZGmio2TcbGtZlVwhCEELWYDB8j7zabVg7LcOVffVGarAq1C5hTNrFqSdLA6iww._7xji5yoWOHsZQ2GeIy96QTtE2XsbYGveAkcBNbqJWc&dib_tag=se&keywords=Predator+212+main+jet&qid=1776461255&sr=8-15 I'll get back to you on the airbox mounting screws.