CB125S "Susie" Take Two

CALfeRacer

Fat man on a little bike
Well, I'm finally home for the summer and ready to re-start work on my 79 CB125S, my first bike. As some background, I eagerly started my first custom build on a $75 bike, which probably wasn't the best idea. After doing everything in the wrong order in my eagerness to finish it, I ended up moving away to college without really finishing the bike. Now that I've gotten some real riding experience, I realized how much needs to be done to this bike to make it solid. So here goes:
1. Putting on chopped rear fender. In WA you're required to have two fenders. Fender is painted, just need to mount.
2. New seat to accommodate rear fender. And the old one is uncomfortable.
3. CB350 Stator and custom harness. This will give me 12V, making lighting a lot easier. Stator is on the way, working on a harness design now.
4. Clean up "dash" by getting headlight ears, then making a custom bracket for my speedo and idiot lights. Speedo bracket is made, just need to get headlight ears.
5. Rearsets. Stock pegs are bent and won't work with the drag bars. Not doing rearsets anymore
6. Soda Blast engine. It's kinda grimy and since this really isn't a "rat bike cafe hybrid" anymore the engine needs to be properly cleaned.
7. Steering lock. Somewhere along the line a PO cut off the steering stop tab on the frame. I'd rather not smash my nice new painted tank with the bars.
8. Fab a better battery box. Old one is kinda so-so on quality.
9. Tune carb. Need to figure out float height, idle screw settings, and jet adjustments.
10. Get title/registration
11. Other minor cosmetics I can't think of right now.
12. Ride the piss out of it
13. Add items to this list because I'm sure s**t will come up.
I'm excited to get started, and will be editing this list and posting pics, etc. as progress is made. Looking at Sunday or Monday as my first big work days, since it is out at a friend's house. Below is a before pic and how it sat when I last worked on it pic.
 

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CALfeRacer

Fat man on a little bike
Anyone have experience with the shocks DCC sells? I've got my eye on a set of slightly longer than stock shocks that can hopefully do better with my fat a**. Heard RFY shocks can be a bit so-so, wondering if these are any better. Thanks!
http://www.dimecitycycles.com/12-75-inch-retro-slim-black-chrome-eye-to-eye-rear-motorcycle-shock-absorbers.html
 

CALfeRacer

Fat man on a little bike
Re: CB125S "Susie" Take Two

Spent a few hours with the bike on Saturday. Finished shaping the rear fender, working on a design for the speedometer bracket, and figuring out the brake cable length. I'll either be putting in a DCC order or making a trip down to the bike yard in Lynnwood (probably both) by this weekend.
 

1sttimer

Active Member
CALfeRacer said:
Anyone have experience with the shocks DCC sells? I've got my eye on a set of slightly longer than stock shocks that can hopefully do better with my fat a**. Heard RFY shocks can be a bit so-so, wondering if these are any better. Thanks!
http://www.dimecitycycles.com/12-75-inch-retro-slim-black-chrome-eye-to-eye-rear-motorcycle-shock-absorbers.html
Shocks seem to be fine for normal riding. I wouldn't recommend it for racing. I have some for sale but they are probably too long for your application.
 

CALfeRacer

Fat man on a little bike
Sounds good. I don't plan on racing this bike at all haha, If I'm gonna race anything I'd build the CM250 I have sitting in a storage unit... but that's a story for another day. How long are yours? 12.75" is kinda on the edge of how long I want to go. Anything more then that and I'm afraid I'll ruin the geometry on my bike.
 

1sttimer

Active Member
Re: CB125S "Susie" Take Two


CALfeRacer said:
Sounds good. I don't plan on racing this bike at all haha, If I'm gonna race anything I'd build the CM250 I have sitting in a storage unit... but that's a story for another day. How long are yours? 12.75" is kinda on the edge of how long I want to go. Anything more then that and I'm afraid I'll ruin the geometry on my bike.
They are too long for your application, they will ruin the geometry, just like the ruined mine :) I highly recommend some simple hagon shocks from Dave Quinn. Just google his name, call the number on his website, tell him your specs (height, weight...simple stuff), pay him $200 and smile for the next 20 years :)
 

CALfeRacer

Fat man on a little bike
It's been a little while. Between getting a new bike, working, and enjoying the summer it's hard to get out to my buddy's to work on the 125.
I got a "new" speedometer for the bike, looks to be something from a 60's small cc honda. I like it, and it should work. Need to design a bracket for that. Brake cable length is figured out, but the cable ends I had are too small for the brake cable. Need to figure out a cable end to get the front brake on. Considering getting another set of cables and swapping to taller bars. I like the drags, but don't have the equipment to build my rearsets at home, and don't quite like the idea of stock pegs and drag bars on a little 125... We will see on that. Decided to stay 6V for now, based on price and the fact I want to be able to have a fun little bike to putt around on and take to the lake in surf shorts... Unless someone in WA has a 90 they wanna sell me on the cheap ;)
Still haven't placed the DCC order but that should come soon, since I'm about to order some stuff to "streetfighter" my Katana.
 

CALfeRacer

Fat man on a little bike
Last time it ran, it ran ok. Still needs fine tuning done. Honestly have had other stuff getting in the way, so work on this bike has been slow.
 

CALfeRacer

Fat man on a little bike
Ha! The project died off as the summer went on in case it wasn't obvious... But this time I'm gonna try my best to knock out some serious work on it! I'll be back home in a week or so, then work can start.
Decided to take the bike in a less "Cafe" direction. Gonna get a hold of some Tracker-ish bars, straighten the pegs, make a new seat, and probably a couple side covers. More importantly though, I am going to get it running good. This bike has just been sitting around too damn long.
On the topic of suspension, I'm going to try to figure out what stock rake/trail was and what the effects of my new front end and potential new shocks will have on it. The front end I got was from a CM200, and at least 2 inches longer than the stock front end (cant remember exactly, been a long time). Forks are slid up close to an inch in the trees, but its still definitely taller in the front. That's the main reason I'm interested in the slightly longer shocks, hopefully they will level it out a bit.
For now, I'm just sketching away ideas for seats and such, will post as soon as work begins. Hopefully this thread can keep me accountable for actually doing significant work.
 

CALfeRacer

Fat man on a little bike
So, according to some pretty crude calculations with a lot of assumptions, I have figured out the changes in rake associated with various suspension length combos. Assumptions were: Stock trail of 25 Degrees, Stock Front Fork Length 36", and Stock Rear Shock Length 12". I'm not claiming any of these are correct, but I know The stock rear length was close to 12", 25 Degrees doesn't seem ridiculous, and 36" was just a round # that came to mind ::)
Here are the results:
"Stock": 25 Degrees Rake
"Stock with .75 over rear": 22 Degrees
"Stock with 2 Over Front": 31 Degrees
"2 Over Front & .75 Over Rear": 29 Degrees
How did I get these #'s? Drew a common point, in this case the axle. From there drew a 36" arc and a 38" arc in 1:6 scale. Found 25 Degrees along 36" and made a point/drew line. Drew a line parallel to x-axis from the intersection. Drew a line parallel to this about .7" above, to show raised rear height. This # came from the difference between 12cos(15) and 12.75cos(15).
So, with the longer front end I am guaranteed at least a few extra degrees of Rake, which will give me heavier steering but more stability at speed. Higher rear should reduce the rake angle a little bit, and loss of ground clearance obviously isn't an issue since everthing is getting raised ::)
 

Erskine

New Member
SL 125 shocks will do you fine. They are 13.5 I think. TL 125 shocks 14" are too long for the swinging arm travel.
 

CALfeRacer

Fat man on a little bike
Good to know! I'll look for some SL shocks or something in a similar size. Any differences between the sl and cb to look out for as far as chain clearance?
 

CALfeRacer

Fat man on a little bike
Seen some posts about the 125s liking the stock airbox. I put a K&N on mine with a mikuni VM20 (pretty sure it was 20, if not then it was a 22) since the stock carb and airbox didn't come with the bike. I'm not opposed to fabbing up a new airbox if it'll help the bike run better, since I'm planning on making custom side covers/ number plates anyways. I guess what I'm asking is: would I be better off just leaving it as is and tuning it or should I look in to making a new airbox? Or, will a stock box work with the mikuni?
 

maxDTM

( ͡° ͜ʖ ͡°)
I run a K&N with a VM22 on mine without any problems. I guess people prefer the stock airbox because it's less finicky to tune, but I don't notice any kind of performance decrease without it. A stock box will work with the Mikuni if you do go that route.
 

spurlock

Member
maxDTM said:
I run a K&N with a VM22 on mine without any problems. I guess people prefer the stock airbox because it's less finicky to tune, but I don't notice any kind of performance decrease without it. A stock box will work with the Mikuni if you do go that route.
Stock air box with its down-facing inlet duct is designed partly to quiet intake noise but also the rubber "venturi" from carb to air cleaner is typical of performance engines. To me it just seems a safe bet that carburetors will provide best mixture control in all speed/throttle conditions, and intake flow will stay matched to the head, cam and exhaust systems if that venturi to the air box stays there.

But as to K&N filters, this is an interesting study that should ring alarm bells for anyone wanting a filter to actually clean the air:
http://www.nicoclub.com/archives/kn-vs-oem-filter.html

-Bill
 

maxDTM

( ͡° ͜ʖ ͡°)
Interesting read, and you're probably right that the stock airbox will provide optimal mixture control. In my everyday riding the k&n seems to do the job fine, though!
 

CALfeRacer

Fat man on a little bike
spurlock said:
Stock air box with its down-facing inlet duct is designed partly to quiet intake noise but also the rubber "venturi" from carb to air cleaner is typical of performance engines. To me it just seems a safe bet that carburetors will provide best mixture control in all speed/throttle conditions, and intake flow will stay matched to the head, cam and exhaust systems if that venturi to the air box stays there.

But as to K&N filters, this is an interesting study that should ring alarm bells for anyone wanting a filter to actually clean the air:
http://www.nicoclub.com/archives/kn-vs-oem-filter.html

-Bill
This is the post in your thread that got me thinking about it! I don't remember the inside of the K&N but I feel like I read somewhere they have a small venturi built in to the neck, not sure though. I figure some kind of velocity stack to smooth out the air is definitely ideal though.
maxDTM, what is the setup you have on yours? Curious to hear what your jetting/ needle/ pilot screw adjustments are to get it running good for you.
 

maxDTM

( ͡° ͜ʖ ͡°)
I'm running a 110 main/15 pilot with the needle in the lowest (richest) position. Pilot screw is standard 1 3/4 turns out and she idles pretty well. A little on the rich side overall but otherwise a smooth ride.
 
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