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Check the site motoIQ.com for their project scooter engine mods. There are several parameters to consider when retuning or modifying an engine. Consult an experienced engine builder and look at the spec. for industrial engines versus racing applications. We are looking for longer stroke, lower rpm, higher valve lift, and reduced overlap. Polishing, porting, coating components, timing, runner lengths, and jetting changes follow once the first four parameters are established. A longer stroke means a different crankshaft and higher lift, if piston clearance allows, means adding material to cam. A crank and cam from a similar engine of larger displacement might be reground to work. Look at the crankcase pumping method to minimize power loss.
With an air cooled engine alcohol injection is used to reduce pre-ignition when higher compression or turbocharging is used. An external water mist system in the air flow around the fins could help control temperature. Aircraft engines are often air cooled and literature on them may yield some ideas as well.
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