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Hi guys,
I am building a motor for a race, here are the requirements I have to stay within... read carefully as some of this my be weird..
129cc max displacement 4 stroke , carb only no fuel injection, 29mm carb max size measured at motor side of carb,
1 gear only may be used in transmission- no shifting allowed ( I may remove rest of transmission, shift rod, shifter etc)
the bike will be running wide open but needs to get off the start fast also..
the rules don't say anything about porting, polishing, race heads, larger valves , lightening rockers, roller rockers ect.. so please think about this as if you were building something as fast as possible within the requirements. We have a machinist sponsor so porting , decking , lightening ect is all free for us. I am even open to going to JE piston or someone else and having pistons made to get me right to the limit on displacement-
I have been running YX140 previously but we may be traveling to a new race and it has the above rules..
we have had really good luck with the YX (piranha )140 motors, but that was for a very spec racing series where we couldn't do almost anything to the motor except change cam and springs..
I just don't have any experience with the 125 platform- any of the manufacturers except YX; your experience and help is greatly appreciated!
Thank you in advance
 

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With the parts availability of the klx110 motors thats what i would go with in your situation. Anything you can imagine the klx platform has it. You could play with the displacement limit by going big bore short stroke, or since you can only run one gear maybe benefit from a stroker crank and slight bore increase to have more torque available lower in the rpms. You can find 4v race heads, big cams, really anything.
 
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