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These engines come with inadequate port durations for the exhaust and intake port. They limit both power and RPM. The transfer durations are OK. I recommend raising the exhaust port for at least a 150 degree duration for the 48cc and to at least 165 degrees for the 66cc. Go to this page to read the best way to figure out what your engine has: http://www.dragonfly75.com/motorbike/findduration.html
And go to http://www.dragonfly75.com/motorbike/blowdown.html to read more about the relation of port durations to peak RPM and to download my free porting calculator (an Excel spreadsheet).
The best all round port duration for the intake is 120 degrees which requires lowering the bottom edge of the port a bit. I use the Black&Decker RTX 3 speed rotary tool with cutting discs that is sold at Walmart. I also use a digital caliper which is also available at WalMart.
And go to http://www.dragonfly75.com/motorbike/blowdown.html to read more about the relation of port durations to peak RPM and to download my free porting calculator (an Excel spreadsheet).
The best all round port duration for the intake is 120 degrees which requires lowering the bottom edge of the port a bit. I use the Black&Decker RTX 3 speed rotary tool with cutting discs that is sold at Walmart. I also use a digital caliper which is also available at WalMart.
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