CR125: RPM 139 or Varner 134

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10/25/2017 9:50 AM

Any members have experience with big-bore 05-07 CR125's? Love the handling, Honda quality, and ergos - just needs a little more oomph! I've ridden 150SX's and know it will never compare, but something in-between would be ideal...Thanks in advance for the tips and tricks!



Build thread here so you know it's not a roach: http://www.vitalmx.com/forums/Bike-Builds,46/Last-New-2007-CR125,1324904

Already jetted well (for the OE Mikuni) with a VForce3, stock pipe/silencer, and one tooth up (53) on the rear to lug me around...

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10/27/2017 2:24 AM

Nobody? I’m interested too...

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10/28/2017 8:01 AM

I'd go Varner or Harris Performance. Varner because he has decades of experience with the CR125 and knows the engine well or HP because of his ability to study and understand the CR125 motor. As a person with a mechanical engineering degree who has dabbled in combustion theory, heat transfer, fluid dynamics, and computational fluid analysis, I'll say Harris blew me away with just how well he knew the CR125 engine and his modern approach at developing his porting packages. He's using techniques that the factory race teams were using minus a $100K CFD program. Not sure how Terry does it these days.

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10/28/2017 8:51 AM

I'd suggest going with a known reputable tuner like Varner, TMR or PC. Never heard of Harris Performance company perhaps he's better known locally, but not here in the west coast.


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Speak softly and carry a big stick.

10/28/2017 9:39 AM

I would go with the 133cc option, you can get the 56mm piston from anywhere, vs buying the proprietary 57mm piston from rpm

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10/29/2017 3:05 PM

Bruce372 wrote:

I would go with the 133cc option, you can get the 56mm piston from anywhere, vs buying the proprietary 57mm piston from rpm

Good call - Just checked and 56mm pistons are readily available. As are 57mm's, but it appears the RPM one is specific to their package...134 sounds like it maintains the revs better than 139.

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