I had the same issue with my SYM Euro Jet, I had cleaned the carb and exhaust. However still bogging out, I took it in to a shop for service, they said sell for parts.
What I ended up doing was replace the seals on the Piston head and Exhaust myself and it has been running fine for another $8000ks :-)
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== Update ==
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I have also fallen victim to cheap 2stroke Oil, which was found to cause buildup on the Spark Plug and in the Exhaust. Never again
I had the same issue with my SYM Euro Jet, I had cleaned the carb and exhaust. However still bogging out, I took it in to a shop for service, they said sell for parts.
What I ended up doing was replace the seals on the Piston head and Exhaust myself and it has been running fine for another $8000ks :-)