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Old 10-17-2008, 08:34 AM
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Ghost0 Ghost0 is offline
Motorized Bicycle Elite Member
Join Date: Mar 2008
Location: Bellingham, WA
Posts: 764
Default Re: i think my "80cc" has issues. top speed only 28mph with shifter kit...

Excellent advice Joe. Start small and work your way up. So far my engine is completely stock. I have done nothing to the engine. I have matched my intake and exhaust headers. Added a tuned pipe and air filter. I have also rejetted the carb. I can now do 35 easy and can hit 40 if there is no wind. Once you get to around 30 resistance, mostly wind resistance, plays such a huge roll and increases exponentially with every mile an hour faster you go.

Have you tried different gears for top speed. For instance I have a 6 speed cassette and my bike will actually get a higher top speed in 5th gear. 6th is just too tall for the engine to pull. I will do some proper porting soon. Plan on trimming the piston skirt to unblock the intake as well as lower and widen it slightly. I will also raise the exhaust port slightly. But like Joe said a little at a time.
Design is easy, execution the hard part.
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