New honda cb 125e

urastus

Active Member
Hello. I have a new cb 125e. I really like riding it. I have made a few changes to better suit me. I would like to share these, and if anybody has any suggestions, I'd be thankful. I haven't found much information.

I have fitted fairly standard enduro type bars. They are the highest I could get for 22.5mm bars and 800mm wide. I had to remove the brace so that I could use the ignition key.

I have since found pro taper adventure bars. Still 800mm wide but higher. Because they are 1 1/8" wide they aren't braced. I have some adapters coming to change from 22 to 31.8mm. I won't make this change until and if I bend the bars on there now. I actually like the height of the bars now.
I have also fitted a puig screen. It looks good and is great when it is windy. Getting behind the screen when its windy is so much easier on the motor; it just purrs.

I find the front suspension woeful. I tried to find stronger springs but can't. I'm too lazy to pull out the existing springs, measure them, see if I can find something printed on them and then contact race tech. I did manufacture some spacers, just under 14mm. The top cap on the forks screws in a couple of mm before applying pre load. Originally there iis probably about 1cm of preload. Now it has about 24mm. Not a great improvement surprisingly - they are still soft, but I haven't ridden it yet.

I have the rear at max pre load. It feels OK, but I reckon I'm still bottoming it out. I'm about 85kg with gear.

I've removed one of the two horns, the dicky bar end weights. I was going to take off the centre stand, but I'm seting this up as an all rounder and adventure bike. It's really easy to do this because it is mostly already there. Such a neutral bike; it is great to stand up on, has a good low gear, very easy clutch to play with in technical stuff. Back to the centre stand: the ability to change tyres in the bush, especially on the front, makes the stand look pretty good.

I have made up a reasonable tool kit and have just received some pretty good panniers. Just light stuff is going in the panniers and I'll only use the panniers on extended trips, otherwise just a day pack.

to do:

Fit the ixil exhaust.
Fit the sigma carby kit.
Open up the air box or look at getting a universal foam filter and removing the air box.
Fit a chain oiler, so that I don't have to worry too much when I'm on forestry roads.

I'll post photos and give some progress, just in case someone else is looking for info on these bikes.

Any specific details about a potential fork spring upgrade would be great. Or any intake info (good filters, remove the air box or not, take the top off the air box?)
 
I also removed pillion pegs. I had to leave the pillion peg mounting plate on the right side, because it also supports the exhaust.

These photos show the exhaust (just fitted), screen and handlebars. I like the exhaust - it gives a nice note but is not loud. There is a leak where the header pipe goes into the head - I suspect it is te copper washer (a crush type?). I did some research and it looks like that, I hope.

The forks are still too soft. The next time I have the bars off I'll lift out a spring and measure it, then try the race tech catalogue to see if they have something heavier but similar dimensions.

I added an extra mount point for the screen. Originally the screen just mounts on the two bolts that hold the headlight on. Going over corrugations I noticed the screen would flex back and forth a fair bit. I used a piece of foam that came off the handlebar cross brace and zip tied the screen to the front of the instrument cluster with the foam roll providing some flexible support. It isn't elegant but very effective.
 

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Yes the exhaust gasket is a $4 copper crush washer. If you haven't fixed that yet you should. You might try tightening the header SLIGHTLY. Use the proper tools.

Holy tornado I want one of those. I would place a 233cc engine in and promptly ride wheelies everywhere.
 
Thanks for the confirmation Damon.

I live in Tasmania, Australia. I thought these bikes were pretty universal.

I love it but it really still feels restricted, which is why I want to open it up a bit. It isn't "free running" if that makes sense. I rode my girlfriend's suzuki address 110 home from Hobart, and it felt quite comfortable on 80km/h. The cb feels comfortable on 60km/h. It is such a good neutral bike though, easy to stand up on in rough stuff, or ride the clutch, brake, throttle for slow manouvreing, and then great to get a knee down on really small tight corners. And 18" wheels are a good all rounder. And the gearing feels spot on; although an extra gear up top would be perfect.

I was going to get heidenau 90/90 18 scout front tyres for both ends, but I like the dedicated road rubber. These things don't really spin the rear wheel.

I want to use this as an adventure type bike; an all rounder. No huge changes. My girlfriend has just got her licence and a scooter. The cb was originally for her, but it was just too big for her to manage or get a foot on the ground (she is 4'11", or 150cm). Having the cb means I can ride with her and not get bored. I rode the cb home for her when we first got it, and was considering getting one too, so things have worked out nicely. I have other bikes (ktm 990 smt, suzuki drz 400e). I can practice slow things on this that would cook the ktm - 60km/h on the ktm and the cooling fan soon comes on, which is why I speed on it :)

My girlfriend can stand up on the pillion pegs of the scooter, which makes it usable as an adventure bike. In the picture she is actually standing up :) This is her third ride (yesterday).
 

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I have been holding off installing the sigma jet kit until I replace

the leaky exhaust header gasket. New gaskets have arrived, but I'm

away.

I have been pondering the air intake. Because we are riding mostly

forestry roads for a while, I want to replace the stock paper filter

with an oiled foam one because I believe they filter dust better and

breathe a lot easier.

I can't find one for a cb 125e. So I'm thinking of trying to seat the

filter cage and filter from a drz 400e. I have some spare drz filters

at home and will pinch the filter cage off the drz. I think it should

not be too hard to make it fit over the intake hole in the air box.

I then want to open up the top of the air box; probably just take the

top off it. Part of the airbox is also the rear mud guard - if I remove

it everything that comes off the rear tyre will be thrown straight at

the filter and rear of the upper engine.

Any thoughts or warnings will be appreciated. I'll try to find a

picture of the drz filter assembly :)

I found a picture of the filter. It is shaped like the base of a cone cut off part way up (or a square edged dome). There is open space inside the dome. It is a foam dome. The dome shape is supported by a plastic framework that fits inside. This dome filter fits over the air intake hole.

I found another picture (different angle) of the filter which shows the shape and internal space.
 

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I'm about to go and fit new exhaust gasket.

Just a curiosity I have with this bike and the drz - its never been a problem with any other bikes I've owned: The bike starts and idles ok. When it is warm it won't rev, it won't work under load. I remembered my drz doing this and I used to drain the carburetor bowl - no doubt I researched this enough at the time to find a fix for the symptom, but never found the cause. Sure enough, I drain the bowl on the cb and away it goes.

I don't think I used to shut off petcocks when I was younger and never had this problem. My ktm and ex dr650 never had this issue, and lots of other bikes from my past. I did consider a vacuum in the tank not letting the fuel run down to the carb, but my drz has a vent hose.
 
Took out the old header gasket. The header pipe is a pipe within a pipe. I have no idea why this is - probably just aesthetic. I'm almost tempted to get a single pipe header made up just so that it is 2kg lighter or so.

I spent an hour or so grinding down the weld where the inner pipe is joined to the outer pipe right near where it connects to the head. Took about a mm off all round.
 
That will help if you make the exhaust more free-flowing;I wonder why they always install such a small diameter head-pipe on exhausts for the 125? The dual-wall pipe .. it would be nice if they only used the outer part.I'm trying to find a muffler shop(I hope they will work on this motorcycle pipe.. many 'auto only' muffler shops will not)not far from me that will bend a new head-pipe out of 1.5" stainless steel pipe to make my little CB125S breathe a bit better;I'm installing the XL185 engine to it w/ a ported head and it needs more.
 
urastus said:
I spent an hour or so grinding down the weld where the inner pipe is joined to the outer pipe right near where it connects to the head. Took about a mm off all round.
Good work. If you notice a power increase from this mod, it probably needs a bigger pipe.
 
grcamna5 said:
That will help if you make the exhaust more free-flowing;I wonder why they always install such a small diameter head-pipe on exhausts for the 125? The dual-wall pipe .. it would be nice if they only used the outer part.I'm trying to find a muffler shop(I hope they will work on this motorcycle pipe.. many 'auto only' muffler shops will not)not far from me that will bend a new head-pipe out of 1.5" stainless steel pipe to make my little CB125S breathe a bit better;I'm installing the XL185 engine to it w/ a ported head and it needs more.

You can go too big. I read an excellent article on this site re tuning (or fabricating) the ideal exhaust for your engine based on things like cc per cylinder and size of exhaust valve, and where you want your torque. There is an equation to figure out the length of the exhaust.

I've heard the term "back pressure" since I was a kid - doesn't describe anything. To summarize part of that article: as the exhaust pulse travels through the exhaust pipe, it causes a vacuum to form behind it. This vacuum then helps drag out the next exhaust pulse. So, you don't want the exhaust pulse exiting the exhaust BEFORE the next exhaust pulse.

I hope I've understood it correctly.

The new pipe is bigger diameter. If I got a header pipe fabricated, I'd base it on the size of the inner pipe.

I apologise if you already know this. And, I found the article: http://www.dotheton.com/forum/index.php?topic=64318.msg734257#msg734257
 
That's some heavy reading there urastus and I just caught a piece of it;I would think it's important to tune your exhaust to the length that matches the powerband and where you want that rpm to be..
I was reading a bit on the internet about the 'Bucket racers'/builders in Australia and it gave some interesting reading of what a couple builders said about optimum size dia. & length of the head-pipe and where the powerband will work best. I'm still learning and would like to know a bit more.
 
grcamna5 said:
That's some heavy reading there urastus and I just caught a piece of it;I would think it's important to tune your exhaust to the length that matches the powerband and where you want that rpm to be..
I was reading a bit on the internet about the 'Bucket racers'/builders in Australia and it gave some interesting reading of what a couple builders said about optimum size dia. & length of the head-pipe and where the powerband will work best. I'm still learning and would like to know a bit more.

:) I'd be interested to hear what you do in your project, especially intake and exhaust.
 
urastus said:
:) I'd be interested to hear what you do in your project, especially intake and exhaust.

I have 2) engines I'll be running/swapping between that both have the same stroke(57.8mm)and they are a 1979' XL185S & an 83' XL200R.I have both the cylinder heads on them specially ported by a porting expert in MA. I'll be running either the XL185 stock camshaft or the XR200R in my 185 & setting it up for high-midrange torque & cheap fuel w/ a low 9.6:1 compression ratio piston and a Keihin mod.PD65 carb. w/ atomizer plate from a 1977' XL125S and I want to have a muffler shop that's friendly toward bending a 'mototrcycle' pipe bend me a 1.5" stainless steel pipe;I know that muffler shops don't have the ability to make the long,sweeping bends that come on many of our stock factory header pipes but still hope for a few 45 degree bends rather than 90 degree 'sharpies'.I will go by the recommendation of that bucket racer of between 450-500mm long and 36mm i.d. which is about what the 1.5" O.D. pipe has. I imagine right about 480mm(the CB450 dohc stock headers taper from 32mm i.d. at the port & open up to 39mm i.d. at the outlet w/ one long sweeping curve and are780mm long and that CB450 dohc twin has very similar bore & stroke to my XL200R x 2 but much larger valves and ports) in length should be good.. once the end is welded on to the muffler part I'll just 'go-with-it' however it runs.. so Yeah I want to do a Lot more thinking on the length of the pipe and what will work Best ::) I'm beginning to think a little longer will be better for more midrange..
I plan on using that SS custom headpipe on both engines and the XL200R will have an XR200R piston w/ the XR200R camshaft and I'll want the SS custom headpipe to be longer on that one.. possibly 490mm will work best for both engines..
I'm just trying to decide on the length of the pipe from the engine exh. port to the end that fits into a Honda HM319 stock muffler for a 1972 CB450 dohc.
 
grcamna5 said:
I know that muffler shops don't have the ability to make the long,sweeping bends that come on many of our stock factory header pipes but still hope for a few 45 degree bends rather than 90 degree 'sharpies'.

I assumed it would be pretty easy for an exhaust guy to manufacture a header pipe. After reading your experience I remembered a long gone friend who was into drag racing. He was an IT professional but ended up making cutom headers for turbo charged cars. They were elaborate convoluted creations. Could one of these guys do it?
 
urastus said:
I assumed it would be pretty easy for an exhaust guy to manufacture a header pipe. After reading your experience I remembered a long gone friend who was into drag racing. He was an IT professional but ended up making cutom headers for turbo charged cars. They were elaborate convoluted creations. Could one of these guys do it?

Yes,I think they sure could as long as they have the dies for small pipe(1.5" o.d.,etc.)and you know them well. :)
 
Mr grcamna5, I bow to your experience. I can see that I'm going through the same learning curve that you probably went through long ago :) Things look so simple when you're (meaning me) in ignorance. Although I don't think I'll ever get as "in depth" as you - too many other toys and distractions.

These links are for any other beginners like myself; all this information may already be here, although I find reading from slightly different angles helps:

http://www.coneeng.com/pdf/Designing_Building_Motorcycle_Header.pdf
http://www.coneeng.com/pdf/Choosing_Motorcycle_Muffler.pdf
http://www.coneeng.com/pdf/Speed-v-Sound-Vintage-Views-2015.pdf

There's other info there for multi cyclinder systems.

It has made me realise that I want my peak power / torque at low to mid range. The 125 seems comfortable up to and on 60km/h. I could wring its neck to sit on 80, but that just seems a waste of motorbike (and I have a 990 to satisfy my high speed needs). The 125 is still on low kms though and no doubt will loosen up more to the point I feel comfortable going harder without abusing it. Probably not though, it'll probably just run freer up to 60 :). Also I won't bother trying to mod my after market exhaust system; maybe just try to put in a couple more mount points.
 
urastus said:
Mr grcamna5, I bow to your experience. I can see that I'm going through the same learning curve that you probably went through long ago :) Things look so simple when you're (meaning me) in ignorance. Although I don't think I'll ever get as "in depth" as you - too many other toys and distractions.

These links are for any other beginners like myself; all this information may already be here, although I find reading from slightly different angles helps:

http://www.coneeng.com/pdf/Designing_Building_Motorcycle_Header.pdf
http://www.coneeng.com/pdf/Choosing_Motorcycle_Muffler.pdf
http://www.coneeng.com/pdf/Speed-v-Sound-Vintage-Views-2015.pdf

There's other info there for multi cyclinder systems.

It has made me realise that I want my peak power / torque at low to mid range. The 125 seems comfortable up to and on 60km/h. I could wring its neck to sit on 80, but that just seems a waste of motorbike (and I have a 990 to satisfy my high speed needs). The 125 is still on low kms though and no doubt will loosen up more to the point I feel comfortable going harder without abusing it. Probably not though, it'll probably just run freer up to 60 :). Also I won't bother trying to mod my after market exhaust system; maybe just try to put in a couple more mount points.

I'm just now learning about this urastus;I'm going by what that Aus. bucket racer uploaded :D
Good to see those links you posted.

Typically the short stroke(49.5mm?)engines don't have that much midrange or low end power but Do need to be 'wrung out' to give you their performance.
 
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