New to DTT, and starting a '73 CB125 cafe build!

[nrcb125]

Hey everyone as the title suggests, I'm new to DTT and I picked up a CB125 today. The idea is to build a very basic cafe racer. As of now the plan is to clean everything really well, then make a fiberglass tail-section and put some of the finest Chinese clip-on handlebars on it. I may CNC some rearsets for it as well once I get a chance to sneak into my university's machine shop.

Are there any CB125 quirks I should look out for?

And here's a photo!

 

[joeyputt]

Welcome to Dotheton Brother! Congratulations on your new bike, she looks like she is in really good condition!

 

[VonYinzer]

The 125 is as simple as a four stroke can be. Great first project.

If I can suggest something though... Forget buying some shitty chinese crap parts. If you can cnc rearsets, you can make your own clip ons. Make your own parts any time you can, and if you can't keep your money local. Clip ons and many other "cafe" parts that you can buy from Asia can be whipped up from better materials by locals (or yourself) for the same or in many cases, less money.

Ok, off my soapbox now. Keep us posted on the build!

 

[Rat_ranger]

The dent in the tank is in a great spot to base knee dents off of. You can find about anything you want for that motor, but for a starting point that is a nice clean bike.

 

[nrcb125]

Day 1 Update:
My afternoon class was canceled and I got out of lab 2 hours early so, time to get working! The bike wasn't running when I picked it up, but did have good compression. The PO said the battery was dead. It sat in a charger while I went to work cleaning the carb and tank. The good news: there was no rust in either. The bad news: the copper fuel filter inside the petcock had started corroding leaving nasty green residue everywhere. Cleaned everything up and put everything back on. Got her started and she purrs like a kitten.

The throttle cable seems to be stuck and I'm not sure what to do about it. Going to try cleaning/lubing the cable. Any other ideas?

Day 1.5 Update:
I got the throttle working. Some cable lube had to be applied to the slide in the carb to get it unstuck. I had a bit of trouble with the petcock reassembly and there's now a gallon of gas in the driveway... But, she runs! And pretty well. The last thing to do is adjust the jetting so she'll idle without the choke fully engaged.

 

[nrcb125]

So far I have:

• Replaced the oil
• Troubleshot the electrical system (grounded where it shouldn't have been)
• Troubleshot the carb and found the float had holes in it. The entire carburetor was replaced the carburetor with a cheap Chinese one as it was only $5 more than a replacement float
• Realized the front brake is absolute garbage

After looking into fixing the front mechanical brake or replacing the front wheel with disc for one with a drum brake, I decided to ditch all of it in favor of a hydraulic setup. By chance I had a complete '95 Ninja 250 front brake setup. A simple bracket should make everything fit nicely.

I'll keep this thread updated with everything I do.

 

[nrcb125]

Another update:
I've measured and modeled what would need to be made to fit the Ninja 250 front brake caliper to the CB125S and plan on having the on campus machine shop make it in their CNC machine for cheap. Attached is a rough model of it in Google Sketchup.

 

[nrcb125]

I decided to nut up and buy some XR100 forks for my CB125. They should be here sometime next week. The good: same tube diameter as the CB125, same axle diameter, and a hell of a lot more spring options. The bad: the fender mounting holes may not line up, the forks are definitely going to be longer, and I'll need to redesign the front caliper bracket. It's going to be interesting to see if the XR100 forks work.

 

[mbott]

Awesome! I'm pumped for you and your build!

I recently started a 125s build but it's pretty bare-bones. I got it running but with no seat, electronics, speedo or tac. The thing was a tracker so it was essentially a blank canvas.

I have never done mechanical work before and I have no reference for what a cb125s should look like. Can you please send me some pics of the wiring and electrical system on your bike? Also, in my photo, what is the thing circled and highlighted in red? What is it attached to on your controls and what is it's function?

 

[nrcb125]

I think, and someone please correct me if I'm wrong, it's the tachometer cable. On these bikes they're driven exactly like a mechanical speedometer. As far as wiring, my bike is pretty much bare bones as well. There's a huge rat's nest of wires in the headlight bucket. Pictures won't help you there. I found a link to the cb125s service manual here on dtt. It'll be at the bottom of this post. Hope this helps you!

As an update, the XR100 forks fit! But the top of the triple tree is completely different so there's no way to mount them... I spent a few minutes on ebay and found an XR100 triple tree, steering stem, bearings, etc for only $25. I also snagged some .41kg/mm from BBR for the XR100 forks. Everything should be here next week!

Link to CB125S manual:
http://www.dotheton.com/forum/index.php?topic=20352.0

 

[crqcycles]

Awesome! I'm pumped for you and your build!

I recently started a 125s build but it's pretty bare-bones. I got it running but with no seat, electronics, speedo or tac. The thing was a tracker so it was essentially a blank canvas.

I have never done mechanical work before and I have no reference for what a cb125s should look like. Can you please send me some pics of the wiring and electrical system on your bike? Also, in my photo, what is the thing circled and highlighted in red? What is it attached to on your controls and what is it's function?

Mbott; that definitely is the tachometer mechanical cable!

 

[crqcycles]

Hey everyone as the title suggests, I'm new to DTT and I picked up a CB125 today. The idea is to build a very basic cafe racer. As of now the plan is to clean everything really well, then make a fiberglass tail-section and put some of the finest Chinese clip-on handlebars on it. I may CNC some rearsets for it as well once I get a chance to sneak into my university's machine shop.

Are there any CB125 quirks I should look out for?

And here's a photo!

Hey man!
Like I always say: Nice to see more people messing with small displacement bikes!
I'll be reading this quite often and welcome to this site.
Cheers from Mexico,
Juan Fco.

 

[nrcb125]

Another update:
Got the .41kg/mm springs from BBR today and put them into the XR100 forks. It only took me about 30 minutes. ;D Tomorrow the triple tree should be here. I've also decided to switch to a drum brake front wheel as the XR100 forks don't have anywhere to mount a brake caliper to and I'm not comfortable welding them on myself. More pictures tomorrow or Thursday!

 

[nrcb125]

Update:
So the XR100 triples fit, but the steering stem is a bit too short to be able to secure the top triple. Oh well :-\ As a plus, the steering stem bearings are an exact fit to the CB125S. Not too bad considering a new set of steering stem bearings can easily cost $40. I replaced the CB125S bearings with the XR100 bearings and packed with fresh grease. I've got two options to get the XR100 forks to fit as of now:

1. I can machine custom bolts to fit replace the XR100 fork bolts so they fit into the CB125S upper triple.

OR

2. Bore the holes in the current CB125S upper triple to accept the XR100 fork.

What sounds like a better plan to you guys?

 

[nrcb125]

Update:
I purchased a 1980 CB125 as a parts bike for $100 and have begun moving things from it to my CB125S. Here's what I've done:
-Swapped the triple tree. It fit perfectly.
-Put in the XR100 forks. I highly recommend XR100 forks + .44kg/mm springs from BBR for anyone else with a 1980 and up CB125S. The only issue is mounting the fender. I'm probably not going to mount it.
-Swapped the disc brake front wheel for the 1980's drum brake wheel. Fits well with the XR100 forks.
-Swapped the instrument cluster. The wires from the old to new are all the same color so it's a really easy swap. Only issue is the mechanical tach cable from the '73s engine. Going to make a plug for this.
-I finally got the sucker titled! It only took 6 weeks for the Virginia abandoned vehicle process and a few hours at the DMV.

To do:
-Replace or repair front wheel spokes (they're rusted and I don't really trust them)
-Clean oil filters, replace drain plug crush washers
-Buy 13.5" RFY shocks for the rear
-Install K&N RU-0160 air filter
-Replace fuel line and add inline filter
-Replace or rebuild petcock. The rubber gasket, o-ring, and screen filter are trashed and need replacing.
-Swap front tire from the old rim
-Replace battery with capacitors
-Seat loop + fiberglass a tail section
-Paint. I can't decide on a color. I'm think British racing green or keeping close to the stock orange. Any suggestions?
-Register/insure the bike
-Ride the bike

Pictures next time!

 

[rupaulpierce]

So lemme get this straight... XR100 forks are a bolt on for the post-1980 CB125 triple tree?

 

[nrcb125]

So lemme get this straight... XR100 forks are a bolt on for the post-1980 CB125 triple tree?

They are for 1980 and up.

The XR100 forks are 27mm in diameter, so they'll go right into the triple tree. To double check make sure you have the clamp-type upper and lower triple (pictures to come later). The XR100 also has a 12mm axle so you can reuse your CB125S axle and castle nut. The spacers seem to fit very well with no modification. Lastly, the XR100 has a front drum brake so the CB125S front drum fits in quite nicely.

However, there are a few things to note about the XR100 forks:
1. You will not have a front fender.
2. They are about an inch longer.
3. They have a leading axle so the wheelbase will be slightly longer.
4. You'll have a bit more front end travel
5. I was recommended by a guy who does nothing but dirt bike suspensions to use 30W fork oil for road use. Also, the XR100 forks only need about 3oz each so a quart bottle of fork oil will be more than enough.

I have a hunch that the XR100 fork springs will fit right into the CB125S forks. I'll verify this when I get home from work.

I've also been doing some preliminary research and it seems up to 31mm forks are possible based on the triple trees which accept the same size steering stem bearing as the CB125S. It's unclear as to whether or not the steering stem itself would be the right length.

 

[nrcb125]

Update:
-Decided on a paint color, going to use the same red as the 2012 CBR600RRs
-Put the K&N RU-0160 filter on and it works great
-The fiberglass seat may not be happening because the brat look is growing on me.
-The rim and spokes from the donor bike are rusted to hell and I don't feel safe using them. It leaves me with three options which are all about the same total cost:
[list type=decimal]
[*]Buy new spokes and rim, lace the wheel, pay the local shop to true it and put on the new tire. Most labor on my part, but I know it will work.
[*]Maybe use a CB360 caliper setup, but this would involve combining the bottom ends of the donor bike forks with the XR100 fork tubes which might not even work. Moderate labor, lots of money to be spent on something which isn't proven.
[*]Have a custom bracket machined to fit the Ninja 250 front caliper I already have. Least labor on my part, highest risk as I don't trust myself to do the measurements accurately and one f&#$ up would ruin the whole process and have me out all that money with nothing to show for it
[/list]
I'll probably go with the first option but I hate that it's so boring.

 

[Jzelt]

I'm not sure that's a 1973, I thought the 1974 was the only year that came in orange with the front disc.

Beside the point! Real nice looking bike you have there, I've got one I know the ins and outs of. So I'm really excited to see one get cafe'd!

I'd suggest what the other guys are suggesting though, try not to go real cheap on parts unless you're on a super strict budget.

But! Shoot me a PM if you want to sell those bars, sidecovers, and exhaust, I'm in need of those parts for the resto I've been finishing up of my cb125 haha. Great bikes though, perfect for shooting around town.

 

[nrcb125]

I'm not sure that's a 1973, I thought the 1974 was the only year that came in orange with the front disc.

It IS a '74. But I went through the abandoned vehicle process here in Virginia before I knew any better and the date of manufacture on the VIN plate said '73