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2002 CR125R Keihin PWK Install Question

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Hello All! After searching for days, I'm giving in and need help!!!

I have a 2002 CR125 I am installing a Keihin 38mm PWK carb on. The carb I have is a screw top type and is 91mm from inlet to outlet and fits into the reed manifold perfectly. The carb is 16mm longer than the stock Mikuni TMX and the big bell (inlet?) is 62mm in diameter and doesn't fit into the air intake boot. I rather not stretch it and create a problem down the road, so.....My question is, what intake boot from which CR model will suit this setup best? If anybody can stear me in the right direction, you would be helping me tremendously!

I am also addressing the leaky intake box. I've tried grinding the nubs and sealing with RTV silicone and adding lots of grease around the mating surface,still found a little sand in the intake after 2-3 rides. Ordered a metal plate from an earlier model and will use an older filter cage also.

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No ideas? What is the intake bell diameter of the PWK's off the 99/00 model CR250's? If anybody knows, that would help out alot!

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I ordered an intake boot from a 1999/2000 model CR 250. Will keep this thread updated with the results of this setup for those who may be interested

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Sorry, I can't help with your question, but I'd definitely be interested in hearing a review after you ride with the new carb. It seems there are lots of guys that rave about the PWK for the CR250, but not a whole lot of people who've tried it on the 125 so I've been hesitant to take the plunge. Good luck!

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I've heard many good things from switching to the 38/39mm PWK's across many different makes and models concerning 125's. The 125 is an engine that needs high RPM pushing to keep it moving. The 38/39mm carbs provide this flow at the expense of losing some low RPM response. A 125 makes no low end power to begin with so I am willing to sacrifice that "luxury" which really doesn't exist! The KTM 125 SX is the class leader in power and uses a 39.5mm PWK. After I open up the reed manifold and open the restrictive D shaped exhaust outlet on this bike, it should really pick up some power I'm hoping. My cousin has a 2002 Suzuki RM125 with a fresh build, just like mine and the Suzuki out pulls the CR by alot

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should have gone to a late model 05-07 airboot. Drill the airbox. Dont know if it would help your boot size issue, but I have one on our 02 and it slides on just fine.

Then you need to do the squishband on the bike also before any porting.

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I thought about the 2005-2007 air boot, but I believe it extends a little too far toward the engine due to it being made for the 90mm long Mikuni body, whereas the 1999/2000 CR250 had a Keihin with the 105mm body from bell to inlet. Also, the boot *should* fit the Keihin bell perfectly since the boot was made for the PWK in the first place. The 2002-2007 125 boots made for the Mikuni is a bit of a stretch to fit the PWK's since the PWK has a larger bell.

What carb do you have on your 2002 125?

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So I mocked up a 2000 CR250 airboot fitted to the 2002 CR125 airbox, using a 38mm PWK with the long body and everything alligned and fit well. Just finishing up the airbox now to accept the older filter mounting plate for a better seal. Will post pics when its done if anyone needs them

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we have the stock 36mm mikuni on the 02 bike. Works well for me since it is more of an on/off switch. But my boy will be riding the bike this year as he is stepping up from his CR80. So might think about a PWK swap for a bit more low mid power and usability.

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I've heard many good things from switching to the 38/39mm PWK's across many different makes and models concerning 125's. The 125 is an engine that needs high RPM pushing to keep it moving. The 38/39mm carbs provide this flow at the expense of losing some low RPM response. A 125 makes no low end power to begin with so I am willing to sacrifice that "luxury" which really doesn't exist! The KTM 125 SX is the class leader in power and uses a 39.5mm PWK.

While it's true that KTM produces one of the most powerful 125 out there, just realize that

KTM puts a 39mm carb for its 125 SX motocross bike, whereas KTM puts a 36mm size carb

on its woods enduro race bikes, the 125 EXC.

If you're riding woods on a 125, you're better off w/ a 34-36mm carb. Eric Gorr even says that in his 2 stroke tuning book.

A 39mm carb on a 125 is only applicable for either motocross or flat track racing.

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I'm well aware that a 36mm carb gives better low end power but any 125 out there doesn't make enough low end to justify starving out top end pull for the measely bottom end response that may be picked up. I have a YZ400F for woods if I need bottom end power. I want this CR to be light and pull on top. The way Honda designed it is shameful. The bike falls flat on its face compared to other 125's when revving out

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I'm well aware that a 36mm carb gives better low end power but any 125 out there doesn't make enough low end to justify starving out top end pull for the measely bottom end response that may be picked up. I have a YZ400F for woods if I need bottom end power. I want this CR to be light and pull on top. The way Honda designed it is shameful. The bike falls flat on its face compared to other 125's when revving out

+1 on this. I think the low end loss is negligable and can be made up elsewhere. the 38mm pwk makes the 125's really scream. I love it on my 94 cr144.

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On 3/7/2012 at 9:40 AM, Coonass400 said:

So I mocked up a 2000 CR250 airboot fitted to the 2002 CR125 airbox, using a 38mm PWK with the long body and everything alligned and fit well. Just finishing up the airbox now to accept the older filter mounting plate for a better seal. Will post pics when its done if anyone needs them

5 year old thread but if you have pics of the whole setup that would be great. I'm a little skeptical of the 00 250 airboot on the 02 125 air box. 

 

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