Honda CR125 1991(dyno video + charts) + CR125 1992 + YZ125 1996

NiekL
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NiekL 6/25/2019 10:53pm
6/25/2019 10:53pm
Having a lot of fun with the bike. I don't ride it that much, keeping her cleanWoohoo

Working on a CR125 1992 in peak colors now! I also builded a 1992 CR125 in oem colors last year, will add some pics later.

Riding the CR125 in Holland
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sandman768
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sandman768 6/27/2019 4:04am
6/27/2019 4:04am
Just read through the entire build...great work! Bike is epic!
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neverwas
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neverwas 6/29/2019 1:41pm
6/29/2019 1:41pm
Great build and great build write up,nice work.
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NoMuff2Tuff
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NoMuff2Tuff 7/11/2019 11:58pm
7/11/2019 11:58pm
This is an awesome build, you did a great job!!! I'm a Honda die hard and my 07 CR 125 is down for a rebuild and I will look at doing some of the case mods you did. Compared to my older HPP bikes I've owned the 07 runs strong with the mods I have but still doesn't have the over rev as the HPP motors. Does anyone know why the lost of top and over rev on the 2000 and up CR's. My 2000 was the slowest stock 125 I ever owned, all mid and no top end.

The Shop

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DynoDan22
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DynoDan22 7/12/2019 6:22am
7/12/2019 6:22am
When Honda went to the aluminum frame in '98 the intake tract wasn't as straight as the HPP engines of the past. The intake tract was kinked severely for packaging reasons which took a lot of top end away. Also, the "RC" valve cylinder was developed by one on Honda's road race engineers. The new powervalve was more of a "powerbaffle" than a functional powervalve and didn't seal as well as the old HPP valve. That, along with massive intake port runners once again inspired by the road race team's cylinders left the '00-'01 CR125's running more like a high performance leaf blower than a good running 125. My '01 was a torqueless turd.
NiekL
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NiekL 7/12/2019 1:08pm
7/12/2019 1:08pm
sandman768 wrote:
Just read through the entire build...great work! Bike is epic!
Thanks! I like your builds also, keeping them close to original
NiekL
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NiekL 7/12/2019 1:20pm
7/12/2019 1:20pm
DynoDan22 wrote:
When Honda went to the aluminum frame in '98 the intake tract wasn't as straight as the HPP engines of the past. The intake tract was...
When Honda went to the aluminum frame in '98 the intake tract wasn't as straight as the HPP engines of the past. The intake tract was kinked severely for packaging reasons which took a lot of top end away. Also, the "RC" valve cylinder was developed by one on Honda's road race engineers. The new powervalve was more of a "powerbaffle" than a functional powervalve and didn't seal as well as the old HPP valve. That, along with massive intake port runners once again inspired by the road race team's cylinders left the '00-'01 CR125's running more like a high performance leaf blower than a good running 125. My '01 was a torqueless turd.
Ouch I had the 2001 Cr125 also. I rode the bike stock, and talking about the 2001 here got me thinking! I would never get a good start with the bikeGrinning riding it felt like a slow lawnmower compared to when i ride the hpp now.

Power wise a lot factors make the 2001 slow compared to a hpp. I never understood why Honda went the complete different way after the hpp dominant years. These engines where bulletproof and powerful.

NoMuff2Tuff
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NoMuff2Tuff 7/12/2019 6:12pm
7/12/2019 6:12pm

This is to show you just how weak the early and mid 2000 Honda's were. It's hard to imagine Honda let this happen. I know it was the time when the rave of the 4T were coming in but still. 7-8 HP is hard to even comprehend. Lol. They made some big head way with the 05-07 but it still wasn't a screamer stock.
NiekL
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NiekL 7/13/2019 4:40am
7/13/2019 4:40am
This past year i had a lot of projects. One was the build of a CR125 1992, this bike was on a budget so i had to cut some things out. I builded it for a friend of mine who owns several Honda CR125’s 1987/1989 and now a 1992 also.

I was busy building the bike up, some story as my 1991 but not with all the mods. But again, all engine bearings renewed etc. In the end the bike came out nice. My friend renewed the seat and got the tank refurbished after i took the pics.



First start: https://youtu.be/lqFfnqbqo0U
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twade220
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twade220 7/13/2019 8:15pm
7/13/2019 8:15pm
Our 04 was slow as could be. We put a Boyesen rad valve with a air Stryker carb on it. Big improvement. Next we put a pro circuit pipe and silencer, and an air boot from an 06 on. The bike with the combo of mods is a completely different machine. He had no problem running with the other 125s. People say it's the powervalve we also ran crf suspension on it . setup that makes her so slow but I think the carb made the biggest difference.

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NoMuff2Tuff
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NoMuff2Tuff 7/13/2019 9:53pm
7/13/2019 9:53pm Edited Date/Time 7/13/2019 9:54pm
twade220 wrote:
Our 04 was slow as could be. We put a Boyesen rad valve with a air Stryker carb on it. Big improvement. Next we put a...
Our 04 was slow as could be. We put a Boyesen rad valve with a air Stryker carb on it. Big improvement. Next we put a pro circuit pipe and silencer, and an air boot from an 06 on. The bike with the combo of mods is a completely different machine. He had no problem running with the other 125s. People say it's the powervalve we also ran crf suspension on it . setup that makes her so slow but I think the carb made the biggest difference.

Nice bike, bet it was sweet with the Showa forks
NiekL
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NiekL 7/14/2019 4:12am
7/14/2019 4:12am
twade220 wrote:
Our 04 was slow as could be. We put a Boyesen rad valve with a air Stryker carb on it. Big improvement. Next we put a...
Our 04 was slow as could be. We put a Boyesen rad valve with a air Stryker carb on it. Big improvement. Next we put a pro circuit pipe and silencer, and an air boot from an 06 on. The bike with the combo of mods is a completely different machine. He had no problem running with the other 125s. People say it's the powervalve we also ran crf suspension on it . setup that makes her so slow but I think the carb made the biggest difference.

That bike is in good condition! I like the looks from that generation frame.
twade220
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twade220 7/14/2019 12:49pm
7/14/2019 12:49pm
We ran 06 crf 450 suspension and he loved it. They really are fast when you change a few things. He's 170s and holeshotted a pretty large crowd of 125s. Bike handles great. Like I said we started with the carb and it was night and day difference. Thanks for the comments.
twade220
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twade220 7/14/2019 12:55pm
7/14/2019 12:55pm
Here is a couple other 125s he built.
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twade220
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twade220 7/14/2019 12:59pm
7/14/2019 12:59pm
Here is a couple other 125s he built.

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NoMuff2Tuff
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NoMuff2Tuff 7/15/2019 5:28am
7/15/2019 5:28am


NiekL, when I was looking at your pics with the case porting mods to try and help direct flow to the transfers I noticed the difference in the reed valve angles between the KTM and CR. We know KTM is the latest and greatest and It looks like KTM tries to make more of a direct shot of gas flow into the transfers. For you to make that kind of power with an almost 30 year design is pretty impressive.
MotoStorSD
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MotoStorSD 7/17/2019 9:08pm
7/17/2019 9:08pm
Would love to see those dyno charts! Awesome build you got there!
NiekL
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NiekL 7/18/2019 10:47pm
7/18/2019 10:47pm
I mentioned i was quite busy and not posting a lot, here is the proof:

Together with a friend of mine we rebuilded a YZ125 1996, race ready and full serviced. Technical 100%, not fully restored in cosmetic. This bike should be a ride bike, not a showroom bike. We put on a alloy rear frame and a white airbox. We liked the end result and made a guy happy with the bike he got new at his 18th birtday in 1996! Shipped it out and now i’m working on a Peak CR125








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Pit Row

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450exc115
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450exc115 7/19/2019 6:17am
7/19/2019 6:17am
The YZ looks sharp.. Liked those mid to late 90s bike look as they got away from the glamor of the early 90s. What alloy frame did you use? I have a 02 YZ125 project coming up and wouldn't mind swapping out the steel frame for an Aluminium one. The bike already has the airbox mode to accept the newer rear plastic but it would be cool to run an Alum subframe.

Banana_oil
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Banana_oil 7/19/2019 7:45am
7/19/2019 7:45am
450exc115 wrote:
The YZ looks sharp.. Liked those mid to late 90s bike look as they got away from the glamor of the early 90s. What alloy frame...
The YZ looks sharp.. Liked those mid to late 90s bike look as they got away from the glamor of the early 90s. What alloy frame did you use? I have a 02 YZ125 project coming up and wouldn't mind swapping out the steel frame for an Aluminium one. The bike already has the airbox mode to accept the newer rear plastic but it would be cool to run an Alum subframe.

The 02 already has an alu subframe. Go for titanium! 😉
NiekL
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NiekL 7/19/2019 1:21pm
7/19/2019 1:21pm
NoMuff2Tuff wrote:
[img]https://p.vitalmx.com/photos/forums/2019/07/15/360305/s1200_4069A15F_0A85_450B_9B9F_E915FB3807D8.jpg[/img] [img]https://p.vitalmx.com/photos/forums/2019/07/15/360306/s1200_C59BE168_CE0A_477C_8B55_12ED166813E3.jpg[/img] NiekL, when I was looking at your pics with the case porting mods to try and help direct flow to the transfers I noticed...


NiekL, when I was looking at your pics with the case porting mods to try and help direct flow to the transfers I noticed the difference in the reed valve angles between the KTM and CR. We know KTM is the latest and greatest and It looks like KTM tries to make more of a direct shot of gas flow into the transfers. For you to make that kind of power with an almost 30 year design is pretty impressive.
Yes that's what you see in modern two strokes, straight intakes. The intake manifold angle on for example the latest KTM sx85 is also very straight.
NiekL
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NiekL 7/19/2019 1:24pm
7/19/2019 1:24pm
450exc115 wrote:
The YZ looks sharp.. Liked those mid to late 90s bike look as they got away from the glamor of the early 90s. What alloy frame...
The YZ looks sharp.. Liked those mid to late 90s bike look as they got away from the glamor of the early 90s. What alloy frame did you use? I have a 02 YZ125 project coming up and wouldn't mind swapping out the steel frame for an Aluminium one. The bike already has the airbox mode to accept the newer rear plastic but it would be cool to run an Alum subframe.

A YZ125 2001 subframe and airbox was used. Stripped the paint from the subframe, I liked the bare alu look more.
NiekL
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NiekL 7/19/2019 1:41pm
7/19/2019 1:41pm
Here are some dyno charts from testing pipes. Found a little more midrange power afterwards from trying different needles. The one in these charts was a little on the lean side.


MotoStorSD
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MotoStorSD 7/27/2019 11:51am
7/27/2019 11:51am
Wow that's incredible! You really are not far off from the 18' 125's and in some places you are matching and even beating them in HP numbers.
kalimero
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kalimero 4/14/2020 2:56pm
4/14/2020 2:56pm
Impressive numbers, A good thing to try would be a 91 head and a wossner piston for a 89 cr125 no window, have you tried domed pistons or just stock flat tops? i was always curious if they make a difference, well they obviously do but but what kind of difference more rpm? idk.
Chris99Flannery 4/18/2020 5:24pm
4/18/2020 5:24pm
NiekL what spark plug heat range do you run. Ive gone to 10 on r7376 to help with heat fade a few laps in. Is this a problem you encounter?
TonyD76
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TonyD76 8/22/2021 6:47am
8/22/2021 6:47am
NiekL wrote:
I had some spare cases for the engine, this got me to the idea to modify one set to the more 'actual' two stroke case design...
I had some spare cases for the engine, this got me to the idea to modify one set to the more 'actual' two stroke case design. (Like a YZ125 for example). The YZ125 has a narrow inlet hole at the reed case compared to the later two strokes. Good or not, i just wanted to make 1 set modified cases and keep one set oem. This for me is a good option to learn some more about gasflow in a twostroke. I did some engines before, but not the older two stroke cases. When u never try you never learn!

The stock cases:




Yamah YZ125 cases:


Honda HRC CR125 cases:
The rear transfer port from the YZ125 and the HRC CR125 have a cut out in the lower part after the reed to get the rear transfer port feeded. This can be seen at the right side red marked circle.



The v-force reed i was going to use had a restricted part at the upper part of the reed because of the narrow inlet window:





With that in mind i went to work. Starting with the basic refining of the cases by removing rough edges and materials that came with the engine after the production proces of the cases. This wil improve gasflow for sure.



After that i did the 'hrc' mod.


I finished the cases off with some bead blasting, yes this doesnt look better, but the main reason is that want the oil/fuelmix to create a oil film on the surface of the cases to increase airflow.



Cases ready after painting them together with all the crankcase covers:




Do you have more pictures of the case mods,,thank you

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