Author Topic: CB100/CB125 Hybrid aka CB112.5 (Read 8736 times)

Tugboat · « **on:** July 22, 2013, 01:14:52 PM »

Picked this CB125 up the other day for $250. It's a 1980 model, last registered in '82. Looks like someone had a little spill - bent front fender, headlight bucket has a ding, bent turn signal - and put it away for 30 years. Tank is rusty inside, but other than that the whole bike is in remarkable shape. The motor was frozen though, and the PO couldn't get it unstuck. So he sold it to me sans-motor.

As it happens, I have a CB100 motor in my basement. Turns over, haven't checked compression.. It bolts right up though.

One thing is that the air boxes and their box-->carb tubes are different between the 100's & 125's. I don't have one for either bike. Anyone know if it'll all line up? Or do I need to get the whole setup for a CB100 to make it work?

grcamna2 · « **Reply #1 on:** July 25, 2013, 12:53:31 PM »

I'd get the CB125S tube & adapt it;that's the 1980' CB125S carb. on your CB100 engine in the picture,correct ? I think it'll match up nice to the CB125S airbox that's installed because I believe the head intake port angle is the same.

Tugboat · « **Reply #2 on:** July 26, 2013, 10:00:55 AM »

No, that's the stock carb for the CB100 motor I think. It came to me that way. The throttle cable that was on the CB125 (no carb) still has the cap and slide from the 125 on it. They are both way smaller than the carb in the picture.

Tugboat · « **Reply #3 on:** July 26, 2013, 10:20:52 AM »

Popped the carb open last night. Not pretty! We'll see how it looks after a dip.

Also, did a compression test on the motor.. the needle stopped moving at 180

grcamna2 · « **Reply #4 on:** July 28, 2013, 12:11:25 PM »

Tug,
I still think you might be able to adapt that CB100/125 carb to the stock 1980 airbox using the stock 80' rubber tube..,you might possibly have to modify the tube a bit.I hope you can clean up that carb & check that float too.

DustyRags · « **Reply #5 on:** July 29, 2013, 02:13:58 PM »

In for updates

grcamna2 · « **Reply #6 on:** July 29, 2013, 04:14:40 PM »

How's that CB125S doing Tugboat ?

Tugboat · « **Reply #7 on:** July 30, 2013, 02:17:40 PM »

Bought a battery over the weekend and the electrics all check out. Man that little 6v is tiny!

Couldn't get the float pin out of the carb so I soaked the whole thing. Cleaned up pretty good. Buddy of mine has an extra CB100 carb for me and between the two I should be able to have one good one. Was able to pull the pin after soaking and dipped it again to get up in the float needle passage. Needle looks pretty worn.

The bike didn't come with the CB125 airbox-->carb tube so I ordered a repop from Thailand.. we'll see how it works out. Won't be in for another week or two. In the meantime I've ordered an exhaust clamp & shims, rear muffler mount, carb gaskets & the rest of the motor mounts. Just picked up a spark plug & oil at lunch. Should be able to at least fire it up pretty soon.

I was about to sell this CB350 twin I've been working on but I'm gonna have to pull the head to repair a stripped spark plug hole (not me!!) which sucks.. the bike runs really well otherwise. So it goes. On the flipside, I did pick up a lift from Harbor Freight this weekend. My back feels better just looking at it!

grcamna2 · « **Reply #8 on:** July 31, 2013, 02:20:31 PM »

I'm spoiled by having a lift for a few good years...;wish I still owned it.

Tugboat · « **Reply #9 on:** August 08, 2013, 08:53:09 AM »

The carb that came on the bike didn't have a cap or a slide, and its float needle was pretty badly worn. Otherwise it cleaned up pretty well. A buddy of mine had an extra CB100 carb in about the same shape, so between the two I got one good carb and a good set of extra parts.

While that's been soaking I got around to seeing if I could get the motor to fire. I wasn't getting any spark, so I checked the points and the gap was way out. Set it, got spark, hit the intake with some ether.. it lives.

https://www.facebook.com/photo.php?v=10151768499752236

DustyRags · « **Reply #10 on:** August 08, 2013, 09:16:09 AM »

Nice!

But, um, content unavailable. No video

Tugboat · « **Reply #11 on:** August 15, 2013, 08:56:13 AM »

Got a repro CB125 airbox-->carb rubber manifold from Thailand. The CB100's intake comes from the side of the airbox, whereas on the 125 it connects at the front. Turns out that the tube was a bit too short for the CB100 carb, so I cut it and made an extension out of a 1.25" chrome plumbing extension that I got at a salvage place for $1. Still need one clamp, but hopefully it doesn't leak. It fits perfectly, regardless.

Tugboat · « **Reply #12 on:** August 15, 2013, 09:00:31 AM »

The State Of Affairs:
Valves adjusted
Advance unit cleaned
New points plate installed
Gap checked & timing set
Rear wheel off for new tire...

CB125 exhaust pipe doesn't fit! It must be slightly bigger, which makes sense I guess. The pipe I have is in really good condition too. Bummer - gonna cost me at least 100 bones to get the correct one.

Tons of other parts ordered too.. new front & rear tires, front & rear sprockets, chain, clutch cable receiver, rear brake rod, OEM petcock and some various o-rings & bolts. Still need to get a sprocket cover.

Also, the clutch is locked up. Not surprising since the motor was stored dry. I've gotta get the exhaust first so I can fire the bike up and, after swapping out sprockets & new chain & new back tire, see if I can get it to free up before I have to open it up. No biggie there, just the extra $$ I'd be out for gaskets & a SS Allen bolt kit. So it goes.

WhyNot2 · « **Reply #13 on:** August 15, 2013, 12:08:30 PM »

Watching, as I too am working on a CB100. Just no where's near as good of shape as yours.

Good stuff so far.......keep it up.

RAFster122s · « **Reply #14 on:** August 15, 2013, 01:10:07 PM »

If you have time to wait for shipping, check out Tenavintage.com in Indonesia, Anis stocks some cb100 / cb125parts that could be useful resource. He is a good guy to deal with and supports the S90 crowd.

WhyNot2 · « **Reply #15 on:** August 15, 2013, 01:18:22 PM »

Quote from: RAFster122S on August 15, 2013, 01:10:07 PM

If you have time to wait for shipping, check out Tenavintage.com in Indonesia, Anis stocks some cb100 / cb125parts that could be useful resource. He is a good guy to deal with and supports the S90 crowd.

Hey thanks for that link, sure it will help Tugboat, I can assure you it has helped me already. Darn, I can't believe, a complete new cylinder for 30 bux.

Kewl...........................

grcamna2 · « **Reply #16 on:** August 15, 2013, 02:06:22 PM »

Nice Job on the air intake plumbing Tugboat ! Clean modified.

Tugboat · « **Reply #17 on:** August 20, 2013, 10:00:19 AM »

Working on the tank while I'm waiting on my kick-ass CL100 scrambler pipe to get here. Cost $150 shipped, but a decent CB100 pipe was gonna cost me $130 shipped so I spent the extra $20 and got the cool one. Can't wait!

So the tank was a total rust bucket inside. I forgot to take a "before" pic, but it was pretty bad. PO claimed to have cleaned it once but I'm not sure I buy that. You could hear chunks of stuff rattling around inside if you shook it. So this past weekend I spent about an hour with a hose and some nuts/bolts and got all of that chunky stuff out of there. At first I was concerned that it was a lot of material coming out, but it seems to hold water OK so I'm not planning on lining it if I don't have to.

First, plugged the petcock hole with a little cork I got at the hardware store and put in about half a bottle of The Works toilet cleaner. Filled to the top with water and let it sit overnight. This is what it looked like the next morning:

I drained that out.. look at all that crap!!

Rinsed a few times until the water was running pretty clear. Then I put the cork back in and put in a whole bottle of The Works, along with about a quart of water and a few nuts/bolts. Shook it about ten times - each time for a minute, and with about a 5-minute rest period(!) - and here is the result:

Finally, filled it to the top with water and let it sit overnight. Will see how it looks when I get home. My plan is to drain it and rinse, then hit it with some alcohol to help absorb any extra water, then put a little 2-stroke (premix) gas in there, slosh that around & drain a few times, then put the petcock on and fill with gas. It SHOULD stay clean.. may have a little flash rust but all of this is such a vast improvement over how it was that I think I'd be okay with an inline filter. Stay tuned.

grcamna2 · « **Reply #18 on:** August 20, 2013, 04:18:04 PM »

That sure had lots of rust

;it probably wouldn't hurt to line it w/ something like Redkote..,that will keep it from having the same problem again later.
That rust is notorious for a return performance in a short time & I know you don't want that Tug.

Tugboat · « **Reply #19 on:** August 28, 2013, 01:37:48 PM »

I've been making steady progress. Back wheel came off for a new tire and some new bearings. I've installed new front & rear sprockets and have done a lot of cleaning.

Since the bike lacks a center stand I have it up on one of those race stand things.. here it is set precariously on that and a floor jack so I could get the front wheel off. Brakes look fine. I've installed a new tire & bearings here too. BTW - Shinko tires were about $30 each.

I also picked up a CL100 pipe on ebay for about $150 shipped. The cheapest/best I could find a CB100 pipe for was about $130 shipped, and I think this was worth the extra $20. Needs some light cleaning-up on the back but otherwise it's in great shape.

grcamna2 · « **Reply #20 on:** August 28, 2013, 04:04:20 PM »

Did you start her yet ?

Tugboat · « **Reply #21 on:** August 29, 2013, 03:12:45 PM »

Fired it up briefly w/ starter fluid, but haven't run any gas through it yet. Pulling the clutch apart this weekend and replacing a leaky gasket on the other side, then hopefully I'll be able to start it next week.

Tugboat · « **Reply #22 on:** September 09, 2013, 10:35:09 AM »

I had to buy a front motor mount, as the rolling frame I purchased didn't come with one. Actually, I bought two... This is the CB100 one, mounting to the CB125 frame. It doesn't look like the holes that connect the mount to the frame line up correctly.

And here it is using the CB125 mount. They're different part numbers by the way.

Had to use a ratchet strap to pull the frame forward. I think that this is how it's supposed to be? A stressed member that is more rigid because it's bent.

Tugboat · « **Reply #23 on:** September 09, 2013, 10:41:01 AM »

I took me literally an hour to get the three screws off of the oil centrifugal thingy. But eventually they came out and I was able to free the clutch.

Here it is all cleaned up. I've since replaced all three screws.

So now I've got new gaskets on both sides, along with some new Allen bolts. I bought this kit from eBay user "alloyboltz" - nice kit that is well-packaged and labeled.
http://www.ebay.com/itm/HONDA-1970-75-CB100-CL100-CB125-CL125-STAINLESS-STEEL-BOLT-KIT-/130601714626

Exhaust cleaned up and painted on the back (as a rust preventative) w/ high-heat Rustoleum. Lots of other little stuff that I'm not thinking of at the moment. Anyway, I put a little gas in the tank to wash out some of the 2 stroke oil, and it came out all brown. Rust city, again! So there is definitely some Caswell's in my future. Will have to tackle that when I get back in town in a couple of weeks. But for the time being, I rigged this up and rode around the neighborhood for a bit

grcamna2 · « **Reply #24 on:** September 09, 2013, 02:15:33 PM »

That's a cute little temp. fuel cell.

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Author Topic: CB100/CB125 Hybrid aka CB112.5 (Read 8736 times)