Without the exhaust and not upjettint to compensate the additional airflow it will be too lean , run hot and will damage your engine in a short time . A buddy who drinks too much wrecked his scoot and the pipe broke off . He rode it for almost a month and the exhaust valve head came off and ate up the piston , head and cylinder . Running like that can also cause it to seize up and have the piston crack too . The pipe carries away heat from the engine as well as having some restriction to build up backpressure . I removed my muffler on my Echarm with EFI that adjusts itself and boy it was so loud it reminded me of riding a Honda XR 250 . It did have just a hair more on the takeoff but it lost top end speed .
Running it like you have you may get the valves out of adjustment too . All 4T engines will need to have them adjusted at least once with some requiting this right out of the crate . Here is a shop manual
http://www.chinesescooterreference.c...hop_manual.pdf You may need to get Adobe Acrobat Reader ( it is free )
www.adobe.com look on bottom right corner