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Budget Racer – 2001 Honda CR125

by Derek Harris on 05/14/2009

The 2001 Honda CR125 is a great bike.  Yep, you read that correctly.  While the magazines may have called it “slow”, or “anemic”, or even a “turd”, this author begs to argue the bike is a great buy, and even more so is a great buy for you.

“WHAT!!??!” you ask.

2001 Honda CR125

Think of it this way.  While the Honda was never a desirable bike new in 2001 (or 2000, 2002,2003, and even 2004), and while that automatically makes it undesirable to this day for many, it NOW means there exists a cheap, available, dirt bike.  This makes it DESIRABLE, for you.  We are going to show you how to take a turd, and make it timeless.

Yep, a budget build up, just like in all the hot rod magazines, just like most working Americans actually do in the garage while simultaneously drooling over pages and pages of “works” bikes or big budget time bombs currently found in modern magazines.  No fancy hubs that actually weigh more, no bling levers or wide foot pegs, no anodized uselessness, just plain and simple R&D applied to an old bike to make it not only terribly fun, but incredibly cost effective and COMPETITIVE!

Pro Circuit pipe.

In case you didn’t know, since Honda’s introduction of their aluminum frame, their 125 motor suffered terribly.  In fact, despite arguably the best 125 chassis to this day, in a class where power talks, and slow walks, the Honda just never made the cut.  Some blamed it on the small air box, or restrictive intake tract, some blamed it on case reed induction (how silly…all the 125?s run it!), and some even blamed it on the moto gods for punishing Honda’s hard work in chassis development!

In any case, the motor is your number one area of concern.  In fact, it’s your only concern!

The first step to producing good horsepower is to optimize the stock set up.  This requires testing of various pipes, silences, reeds, jets, and tons of hours screaming at yourself and Honda wondering why the bike just wont GO.

In doing so, you will find that:

Boyesen Reed Block.

BUT YOU WANT MORE!!!!!!  As is the case almost all 125?s, and especially the stock Honda, there just isn’t enough power to satisfy the peanut gallery.  The bike doesn’t do anything particularly well, it has poor bottom, poor mid, a mediocre top, but a poor over rev and snap.  In fact, it’s fairly disheartening!

We decided to take the bike no one else would, and race the hell out of it in the over age classes against 450?s, 250?s 350?s, and anything else some craft vet rider figured he could get an advantage with, and we were going to do it out a no more than 125 cc’s of pure ear pleasing two stroke.

Enter the 2001 CR125R.  We picked this baby up cheap, with a PC pipe and silencer and VForce 3 already installed.  The bike was to summarize….in a couple words, a turd.

VForce 3 Reed Block.

Time for mods.

To do so, we enlisted the help of our local guru, H.P.Bikes for our

-head work
-case work
-brain storming
-head pounding moments

We wanted a complete developmental process, first on a budget, then as our time grew more money would be invested to try and pump up results.

The mods:
The first mod H.P. performed was to throw the head in the lathe and machine off some material for a tighter squish band a more compression.  In the end, the squish band ended up right about 1mm from the top of the piston.  They told us this is a good, safe number for a 125 mx bike, but they also mentioned that on the Honda 125, with it’s use of a head gasket instead of o rings, and the fact the piston sets below the deck at TDC, that to get the squish any tighter, more extensive machine work would be necessary.  While in the lathe, the head also had a positive angle added to the squish band in the range of 2 degrees.  This usually shows gains on the dyno in the upper end of the power band.

We asked them just how tight they go on builds, and were astounded to hear that if the motor was kept fresh all the time, that as low as .7mm can be used when all other elements are tuned correctly.

H.P. then completely disassembled the cylinder, and performed a complete port job.  They altered port timings, bumping the exhaust duration quite a bit, along with changing the intake durations.  They also worked on the cross flows and port widths to achieve maximum cylinder fill, and ultimately power.  They told us the ultimate effectiveness to a cylinder relied completely on how efficiently the ports scavenged and how well the pipe worked in conjunction with this.

We asked for a no non-sense, pro screamer only.  More on this later.

Initially, we had planned on handing over the entire motor, and saying “Here…do whatever it takes!” but instead we started with just the head and cylinder and decided to do a step by step modification process and save that for later, and explained this to them so they knew our approach and goals.

2001 Honda CR125 HP Bikes modified machine. Photo by Kenny Lau - Awesome Shots

First Impression:
The stock Honda tiddler couldn’t really get out of its own way.  This bike not only changed that characteristic, but did so dramatically!  The bike now lifted the front wheel when told to, cleared the tough jumps that the some of the 250f’s were struggling on, and all around hauled ten times the ass as before.  Power to weight was considerably improved!

But then the weather warmed up.  The jetting went from a little rich to pig rich, and the bike suffered.  Wow, jetting is important.  After tons of fiddling, some frustrating rides, and a little head pounding, it was found the motor liked a 340 Main Jet instead of our starting point of a 380!  What a change in performance!

We were happy for a little while, but after some more hours, we found some things to complain about.  The bike still sounded like an older Honda.  Sure it pulled well, but it just went WAH WAH WAH instead of WHAP WHAP WHAP.  Any by standers would have no clue how fast the bike actually was from its sound!  It also seemed to take a while to wind up.  While hard to describe, compared to other 125?s, when in a corner and flicking the clutch, it wouldn’t instantly scream and go, instead it took a little time to wind up and get going (in the rev department).  Lastly, while eye watering fast on the pipe, the power was razor thin.

It was time to get greedy.  We trucked back over to the boys at H.P. and had a nice long discussion about their thoughts, fixes, and ultimately decided on a couple key mods.  We decided in the iterative process to do this in steps, but doing it all at once certainly would have been easier!

WOW.  If you do nothing else to your older Honda, do this!  The sound of the motor changed dramatically while on the pipe, and we are pretty sure it picked up about half a horse everywhere.

Wow, yet again.  This bike definitely likes more air.  In fact, the improvements found by just drilling the air box and fitting the newer intake boot are so impressive we highly suggest to anyone with pre 05 honda to do this prior to reed cage or pipe purchases.

Valve limiting stop stock and modified.

Power Valve modified.

Modern YZ125 Cylinder

2001 Honda CR125 Cylinder

After some extensive epoxy filling and shaping, it was back to the track.

How was it?

In one word: scary.

In two words: scary good.

This is the bike Honda should have built.  On the pipe its easily the fastest 125 we have ever ridden, and thankfully, after the epoxy work, the mid range picked up considerably and the bike was an all around power package.

How does it compare to a modern Yamaha?

The Yamaha has a potent all around motor, with excellent bottom for a 125, impressive mid, and great top.

Our H.P. Bikes Honda has no bottom, acceptable  mid, but a top end to die for!

In a head on drag race from a clutched start, the Honda wins handily.

In roll on drag race, starting lower in the rev’s, the Yamaha gaps handily at first, then gets eaten up once the Honda hits power.

The Unveiling:

Tony P - Number 6 Honda CR125. Photo by Kenny Lau - Awesome Shots

After a couple months of getting it just right, (most of which was spent working….gotta pay of those bills), it was time to debut the bike. So how did it go?  With a nearly full gate of 30 riders, most of which were on 450?s, we knew this would be interesting!  Let’s, hear it from the man himself:

1st moto, over 40 Senior (expert). It’s around 75 degrees and overcast which is perfect for me. I haven’t practiced a start since 1993. I practiced a few before the 1st moto as I’d honestly forgotten how to start on concrete. With the 500, it really doesn’t matter but the 125 is gonna need all the help it can get. I managed to get a great jump coming off the line but I missed my shift to 2nd. Those freaking 450s, it’s like they came out of a slingshot. The start has a big left hand sweeper then it meets the track. Most people drift way outside so I put the old rudder down and cut underneath them and got to the 1st turn in about 4th. It took about a half a lap to pass the other guys and I was able to stretch it out a bit. On lap 4 a guy on a 250 2 stroke caught me and started putting a wheel in but couldn’t seal the deal. I’d had enough by that time and figured I’d settle for 2nd, conserve what little energy I had  left and go for it in the last moto. I went to the far outside and pointed to the inside and let him by. I was thinking he’d run off and leave me but he didn’t. Finished 2nd.

The Honda handles excellently, just needs some work done to the motor. Photo by Kenny Lau - Awesome Shots

2nd moto, It’s now over 90 degrees and I’m finished. I get a crappy jump off the gate and make some up in the sweeper again going into the 1st corner somewhere around 6th. I cut hard to the inside of a 450 and I guess the screaming of the 125 freaked him out cause he grabbed a handful, the bike went sideways and he slammed into the side of me smashing my foot. It sucked alot but at least I didn’t crash. It took me about a lap this time to get into 1st and the guy I battled with the 1st moto pulled off. I thought I might pull it off but then I couldn’t really brake because of my foot. I overshot a small berm and let the front end wash out. Not a big deal since I had gapped 2nd a bit but by then but my foot wasn’t working too good so I wussed out and pulled off. Oh yeah, about the 2nd lap my rear end started feeling really weird. I swapped all the way through the whoops where the bike normally just tracks straight. After the race I inspected it and it’s basically just a spring so something turned loose inside the shock.

Overall impressions.

The bike is fast and I didn’t feel like I was at a disadvantage on most parts of the track as long as I could ride it like it’s supposed to be ridden. Unfortunately for me that’s about 3 laps. I had to basically go where the 4 strokes weren’t going simply cause I carried alot more speed than them and I could ram them on the exit. I had to snatch the bike to one side or the other several times because of it. I still feel it can’t pump enough air due to the intake tract. Our next step is swapping intake boots even if we have to fabricate an airbox. It’s been a fun and exciting “project” to say the least. How fast is it? If you’ve ridden a YZ125, you know it has good bottom, good mid and good top. The “HP Bikes” modded CR125 has virtually no low end, some mid and a hellacious top that will make a YZ125 rider envious. It’s not a slow bike but it requires you to be on top of things 100% of the time. This is the engine I should have had when I was 16 and could ride until the bike ran out of gas. I asked for this style of power and got it in spades. I’m the weak point now.

My favorite question from other riders was “Is it a 125, 134, 139, 144 or a 151?? The answer wasn’t what they wanted to hear.”

It was found that evening he possible broke his ankle in the collision, but is in high spirits to race the bike again!

Huge thanks to the fellows at H.P.  Not only did they turn our turd into a timeless bike, but they did it for a great deal, and delivered exactly what was asked for…now if only we had asked for a tad more mid-range and a hair less top (and realized what we want, and what we need, are often different).
They can be reached at

Hmmm we wonder just how good a 134 can be?

To order photos from Kenny Lau at Awesome Shots.

The H.P. modified CR125 is fast, fun, light and cheap! Photo by Kenny Lau - Awesome Shots