All Things Moto! Dirtbike Forums

Go Back   All Things Moto! Dirtbike Forums > Dirt Bike - ATV - Suspension Forums > 2-Stroke Dirt Bike Forums > 2-Stroke Dirt Bikes - Honda

Reply
 
LinkBack Thread Tools
  #1  
Old 04-29-2014, 10:30 AM
Beginner Class
 
Join Date: Mar 2014
Last Online: 05-01-2014 12:20 PM
Location: VA
Posts: 5
Default 2001 CR 125 help before I sell and buy something else

     

This is my first post but I have read many good posts on this site that have helped me along the way.

I bought a 2001 CR125 a few weeks ago. It is not my first bike but I have been out of riding for 10 years. This is also my first Honda 2 stroke. All my other bikes were YZ's or KX bikes.

The bike was a bit of a neglected basket case but I went through it from one end to the other and it is running well now. It has a FMF pipe and a larger carb but was mostly stock.

I put a set of V Force 3 reads in, new air filter, replaced the air intake boot with a 2007 boot, rebuilt the top end, milled the head, cleaned and rebuilt the power valve, added a 7mm spacer to keep the power valve from closing all the way on the stopper and did some light intake porting/clean up.

My problem before all this work and the problem I still have now is I canít stand how the power band comes on. The bike is slow to rev up with a week low end then the power band comes on very hard and sudden then tops off quick.
My daughters YZ 80 is more fun to ride with a smoother power band and more bottom end.

Unless I can get more bottom end and smooth out the sharp power band I am going to sell it for a loss and pick up a YZ125.

Ideas?
Reply With Quote
  #2  
Old 04-29-2014, 11:28 AM
JMV's Avatar
JMV JMV is offline
Expert Class
 
Join Date: Jul 2012
Last Online: 10-04-2018 10:24 PM
Location: Central Coast, Ca
Posts: 979
Default

You can spend tons of money on your CR125 and it's not going to pull as well as a stock YZ. I have spent tons on money on my 03, have to run race gas and my buddy's YZ125 has a broader, easier to use powerband. Can't beat Honda reliability though. I am very happy with the feel of my CR, would be nice to have a few more ponies, but it's sure fun to ride.
Edit:
Going to a bigger carb, like you said you have isn't going to help your bottom end. Running the stock 36mm carb will help.
Reply With Quote
  #3  
Old 04-29-2014, 11:48 AM
Intermediate Class
 
Join Date: Apr 2014
Last Online: 03-09-2017 01:19 PM
Location: Fairview, Texas
Posts: 210
Default

Larger carburetor?

I would put the 36mm TMX back on. (easiest)
Reply With Quote
  #4  
Old 04-29-2014, 11:58 AM
Beginner Class
 
Join Date: Mar 2014
Last Online: 05-01-2014 12:20 PM
Location: VA
Posts: 5
Default

Thanks for the replys. I cant remember what size carb the previous owner said it was but I wll try to pull some ID numbers off of it and try to look it up.
Reply With Quote
  #5  
Old 04-29-2014, 12:39 PM
JMV's Avatar
JMV JMV is offline
Expert Class
 
Join Date: Jul 2012
Last Online: 10-04-2018 10:24 PM
Location: Central Coast, Ca
Posts: 979
Default

Could very well be a Keihin PWK. That's a popular mod, but if you are lacking bottom end, go back to the 36. They swapped to a 38mm carb in 03 and I have considered swapping to an 02 or 01 carb or going to a 36mm PWK to see how it changes.
Reply With Quote
  #6  
Old 04-29-2014, 02:03 PM
stevo450's Avatar
ATM! Pro Class
 
Join Date: Aug 2012
Last Online: 01-31-2017 07:35 AM
Location: South Australia
Posts: 3,709
Default

Just my two cents here, agreed that the larger carb isn't helping the bottom, not only that but will also cause it to come on hard ( once the larger carb surfaces it's optimum rev range -ie- higher rpms/ powerband range ). Don't waste your time with a TMX unless your strap for cash, the PWK will be much easier to dial in.... Go back to a 36 should help matter....

However there is one 'mod' that hasn't been mentioned, it's kind of a two stroke cheat but works well! The problem with the 125's is the lack of inertia ( in both respects of having a bit more rolling torque*** down low, but also sapping up [easy mans words here] some of the power burst when the PV opens up ). Adding weight to the crank assembly does help, it may/should give the topend a bit 'more'-only because the power curve is slightly delayed in delivery!! Remember your not adding torque ( well, per se ) just increasing the rolling torque capacity of the flywheel and crankshaft.....this mod will ( IMO ) do more than all the pipe mods and porting you can think of, with the exception of the carb-but that's BIG can of worms as to how this works....
Reply With Quote
  #7  
Old 04-29-2014, 02:09 PM
JMV's Avatar
JMV JMV is offline
Expert Class
 
Join Date: Jul 2012
Last Online: 10-04-2018 10:24 PM
Location: Central Coast, Ca
Posts: 979
Default

Not sure what you are suggesting with the flywheel weight. The flywheel weight increases the mass moment of inertia of the crankshaft assembly, thus slowing the engine's ability to make RPM changes. All this does is smooth the power delivery and can help reduce wheel spin. It doesn't change the amount of power produced by the engine at all. The weight can help smooth the hit, but won't increase bottom end. they are typically utilized more on 250s and 500s. Not so much on 125s.
Edit:
One thing that wasn't mentioned is gearing. You can add a few teeth to the rear sprocket, or go smaller on the countershaft sprocket. This will help you pull out of the hole a bit.

Last edited by JMV; 04-29-2014 at 02:16 PM.
Reply With Quote
  #8  
Old 04-29-2014, 02:29 PM
stevo450's Avatar
ATM! Pro Class
 
Join Date: Aug 2012
Last Online: 01-31-2017 07:35 AM
Location: South Australia
Posts: 3,709
Default

JMV....Should have cleared a few bits there, your right, it isn't increasing the engines power. From idle it simply makes the engine slightly harder to stall.... That's what I was getting at-It gives it gives the perception of better bottom...at least that my thoughts. And yes as you stated it smoothed power delivery-which the poster seems to be looking for...

Plus 1 on gearing!
Reply With Quote
  #9  
Old 04-29-2014, 02:47 PM
Hang Time's Avatar
Intermediate Class
 
Join Date: Mar 2013
Last Online: 02-22-2018 08:30 PM
Location: Albany, NY
Posts: 199
Default

I don't think the power valve stopper is helping your bottom end either.
Reply With Quote
  #10  
Old 04-29-2014, 02:51 PM
Beginner Class
 
Join Date: Mar 2014
Last Online: 05-01-2014 12:20 PM
Location: VA
Posts: 5
Default

Thanks very much guys. I did drop a tooth on the front sprocket and it helped but I still have a major sudden jump into the power band. Its like no other 2 stroke I have owned.

Its funny... I can hop on my daughters YZ80 and just love the power curve. Its much smoother.

---------- Post added at 04:51 PM ---------- Previous post was at 04:49 PM ----------

I read so many posts about the power valve 7mm stopper mod doing great things. I made one and tried it but you would think preventing the power valve from closing would hurt my bottom end not help.
Maybe I will pull it and try the bike again.
Reply With Quote
  #11  
Old 04-29-2014, 03:09 PM
JMV's Avatar
JMV JMV is offline
Expert Class
 
Join Date: Jul 2012
Last Online: 10-04-2018 10:24 PM
Location: Central Coast, Ca
Posts: 979
Default

125 have significantly sharper power curves (large power increase in a narrower RPM range) than 250s for example. That's just the nature of the beast. It's possible the 80 has so much less power that with your weight, you are loading the 80 down enough to give the impression of a smoother power delivery when it's really just delivering significantly less power.
Reply With Quote
  #12  
Old 04-29-2014, 05:24 PM
dogger315's Avatar
ATM! Pro Class
 
Join Date: May 2009
Last Online: 05-18-2018 01:08 PM
Location: CA
Posts: 2,514
Default

After reading your post, some Red flags popped up.

A bigger carb is definitely a bad idea for any 125 that is not ported and set
up for big top end power at the expense of power everywhere else. A milled
head/higher compression will provide a bigger "hit" - one of the traits you were
complaining about. Subtracting a tooth from the CS sprocket is the same as
adding 3 1/2 teeth to the rear wheel sprocket. That big of a jump will
excaserbate the narrow powerband part of the problem. Finally, you said
you did some light port work. Unless you know what you're doing, any port
work can alter (not for the better), the powerband.

The 01 CR125 engine was one of the last of the "fire breathing" 125 engines
Honda built. Even stock, it was more than a match for any other 125 at the
time, including the YZ.

You may be better off selling the bike since getting the engine back to it's
designed performance levels may require considerable expense.

dogger
Reply With Quote
  #13  
Old 04-29-2014, 06:40 PM
Beginner Class
 
Join Date: Mar 2014
Last Online: 05-01-2014 12:20 PM
Location: VA
Posts: 5
Default

Good information. Thank you
It looks like the catb is a Mikuni TMX 38 and the choke knob is missing. If I don't sell I may see if I can pick up a new stock head and a 36 mm carb.

Porting is a strong word for what I did. I smoothed a few rough casting marks and polished the exhaust.
Thanks for the feedback.

---------- Post added at 08:40 PM ---------- Previous post was at 07:47 PM ----------

When I was trying to measure the carb I noticed that the choke may have been stuck open the whole time.
I guess I have been away from two strokes longer than I thought.

I removed and cleaned the choke then reinstalled it and got it working again. It may have been stuck open the whole time.

I am going to test ride tomorrow and let you know how it goes.
Reply With Quote
  #14  
Old 04-30-2014, 08:03 AM
FRODAD393's Avatar
Pro Class
 
Join Date: May 2011
Last Online: 03-19-2017 09:03 AM
Location: Dallas TX
Posts: 1,499
Default

I have the same bike, and have done many of the same mods you have. By far the best improvement was throwing out the TMX and putting on a PWK airstriker, 36mm. The power is smoother and it Revs out a bit more like a 125 should. I'm also running a 14T sprocket on the front. The motor has enough torque to pull the taller gear and you won't have to shift as much. I was about to sell the darn thing till I put on the PWK, what a difference a carb can make. Good luck man!
Reply With Quote
Reply

  All Things Moto! Dirtbike Forums > Dirt Bike - ATV - Suspension Forums > 2-Stroke Dirt Bike Forums > 2-Stroke Dirt Bikes - Honda


Bookmarks

Tags
2001, cf125

Thread Tools


Similar Threads for: 2001 CR 125 help before I sell and buy something else
Thread Thread Starter Forum Replies Last Post
Clean 2001 Honda XR50 w/mods-Sell/Trade ccra92 Classified Ads 0 07-15-2011 08:23 AM
2001 KTM 250exc Looking to downgrade or sell burtonbutt1 Classified Ads 0 02-22-2007 04:02 PM
2001 Yamaha 250 Sell/Part out mxroll113 Classified Ads 0 06-22-2005 03:28 PM
my bike: To sell or not to sell brcrk General Discussion 48 01-20-2005 01:53 PM
make company sell bike or i sell bike to company mattdcs General Discussion 4 06-17-2004 04:34 PM


All times are GMT -6. The time now is 02:34 AM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright ©2002-2017, JDub Consulting, Inc. All Right Reserved.