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2003 CR125 Mods, Recomendations, Etc.

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Hi guys, I just picked up a 2003 CR125 and was hoping for some advice on various mods I should be looking into.  Specifically:

 

Recomended squish thickness?

Leave the compression stock or raise it up a bit?

What brake rotors bolt right up to it?  Will the newer CRF stuff go right on?

Front fender/numberplate swap to the newer style possible?  I will be replacing the clamps.

Triple clamp offset recomendations for MX?

Gearing recommendations for MX?

Best bolt on mods - pipes, silencers, reeds, etc?

Pipe spacer? Reed spacer? Power valve mods?

I've heard about the bad airbox seal issue and plan to fix that, what's the best method/product?

 

I mostly ride southern california motocross tracks - Pala, Milestone, Perris, etc.  Any tips or other information is much appreciated, thanks!

 

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First and foremost, the biggest upgrade you can do is suspension. You don't need to go swap the forks or anything major, any good suspension shop can have your suspension set up and toyed with to be set up for your weight and riding style which will alone make the biggest difference out of everything. Motor wise, the biggest you can go without really sacrificing durability is a 144 kit. A 144 kit that's ported right (Eric Gorr does nice 144's) makes a ton of power. It depends where you want it though, if you want low mid or top it can be ported for that so the best exhaust is whatever matches your porting. I went with a 144 with low to mid porting and paired it with the proper exhaust and it made a world of difference, compression is fine however leave it. Gearing is totally dependant on the track and your preference however. After that, go with some reeds and a reed cage upgrade. I personally think Boysen reeds are the best, the best I've dealt with anyways. After that get a boysen clutch and ignition cover, those things look sweet!

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Thanks, but I should have mentioned that I want to keep it a 125 (at least for now).  I have a YZ-250 if I need a bunch more power; I was mostly looking for modifications that make the power more ridable - mid to top rather than raw power.  Also, I should mention that I plan to run 50/50 VP C12 and premium pump gas at 32:1 with Motul 800.  I've got suspension covered, ProValve has done my stuff before and it's always spot-on.  I would race vet-intermediate or so if that makes a difference as well.

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Here is my 03 cr 125 set up

I learned most of it from Gorr.

02 exhaust manifold. It is a d shape and helps with mid to low end

775M05400 wisco piston. This is a rm 125 "flat top" piston. The rm stock piston was domed. But this flat top is .060" taller and has the same effect as lower the cylinder. The head will have to be cut so the taller piston will not hit it. Since you are running about 100 octane you will not need to in large the combustion dome. Just cut the squish .060" deeper. If you were to run 93 pump the, 1.5 cc needs to be cut out df the dome to lower comp and stop detenation.

I left the squish stock at 8mm wide and .030" clearance

This taller piston fixes the 00-03 cr 125's like milling .030" off the cylinder base fixes the 02-07 cr 250's.

power comes on sooner and smoother. With a good mid range pull. My motor still pulls great up top just like it did before, but now I don't have to rev it to the moon to go anywhere. A 38 pwk is a nice complement also. I love this motor now. I have almost as much fun on it as I do on my cr 500 afc.

Edited by Kirkes
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Here is my 03 cr 125 set up

I learned most of it from Gorr.

02 exhaust manifold. It is a d shape and helps with mid to low end

775M05400 wisco piston. This is a rm 125 "flat top" piston. The rm stock piston was domed. But this flat top is .060" taller and has the same effect as lower the cylinder. The head will have to be cut so the taller piston will not hit it. Since you are running about 100 octane you will not need to in large the combustion dome. Just cut the squish .060" deeper. If you were to run 93 pump the, 1.5 cc needs to be cut out df the dome to lower comp and stop detenation.

I left the squish stock at 8mm wide and .030" clearance

This taller piston fixes the 00-03 cr 125's like milling .030" off the cylinder base fixes the 02-07 cr 250's.

power comes on sooner and smoother. With a good mid range pull. My motor still pulls great up top just like it did before, but now I don't have to rev it to the moon to go anywhere. A 38 pwk is a nice complement also. I love this motor now. I have almost as much fun on it as I do on my cr 500 afc.

 

 

Kirkes, a good friend of mine has a '01 CR125 and he may benefit from that set-up. Thanks for the info.  

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My 2002 cr125 is still stock for now (excellent bike!, in no rush to modify), these are just some modifications I have researched....

 

Fork Bladders.....When I open up my 02 cr125 forks I plan on removing the "bladders" Read into this.... http://www.thumpertalk.com/topic/545454-disabling-bladders/page-2 ....and do a search on "disabling bladder" for the cr125.....good stuff.

 

Airflow...... Look into the 05 air boot and airbox mods. These bikes supposedly respond well to airflow modifications. (My stock airbox currently has no problems keeping the dirt out btw)

 

Race gas mix.....What you are wanting to run is exactly what I am currently running(50/50 c12 and pump with 32:1 Motul 800 2t.) Even though my bike is stock, I gave it a try a week ago. The difference between pump and 50/50 has been excellent for me, enough so that I will keep running the $$$ fuel.  Throttle response is much better, power seems to come online a little sooner. I just like how much better the engine seems to run overall.  My jetting did become a little rich now that I am running the 50/50. Not dramatic. Just make note that race gas will flow through the jets faster/easier ect because the specific gravity of race gas is lower than pump. (from what I have read)

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