Author Topic: CB100/CB125 Hybrid aka CB112.5 (Read 8680 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.

Tugboat · « **Reply #25 on:** October 01, 2013, 08:30:48 AM »

Only a couple of weeks until Barber and I didn't think I'd have time to properly line the tank, so I found this one on ebay for $100 shipped. Clean as a whistle inside and the paint is in pretty good shape. No dents.

So with a clean tank & working petcock I was finally able to fire it up and ride it around. It didn't want to idle unaided, though it did run well enough to get me up to 50mph on flat ground. When I got home I pulled the plug: looks like I'm running rich.

I pulled out the air filter & left the filter box lid off to see if that leaned it out - no effect. I had the air screw set to 1.5 turns out.. turned it out another 1/2 turn and that improved it but not much.. still won't idle on its own. I replaced the plug cap - no effect. I know it has stock jetting (105/38) and am pretty sure the float height is correct. A couple of times it would overflow once I shut it off, but not every time and never while running. Static timing was set when I installed the new points plate, though I haven't checked it while running.

cbornotcb · « **Reply #26 on:** October 01, 2013, 03:33:02 PM »

Check out the needle jet Tugboat, they tend to "oval" after constant use, that'll mess up your jetting.
Tiny

Tugboat · « **Reply #27 on:** October 02, 2013, 11:24:13 AM »

Messed around with the carb last night. First, the float valve seat was loose. Problem #1.

Next, I checked the float to make sure it floated correctly. Turns out, one side has gas in it. I have a buddy's CB100 carb with a known-good float in it, so I "temporarily borrowed" it. Problem #2.

Checked the slide needle - clip is in the middle position & the needle doesn't look too worn.

Put it back together & ran it about a mile down the road - still running rich, though it does idle a little better (with some extra throttle and the idle screw all the way in). Still won't idle unaided though.

Double-checked the schematic, and stock mains are #105. I'm running a #110 so hoping to pick up a 105 from the shop today if they have one in stock. Regardless - sounds like there are at least two more problem here right? (1) It should idle if the idle jet is correct and otherwise unblocked [jet is not stamped, so not sure if it's #38 like it's supposed to be. Must be aftermarket]; and (2) running rich in the upper throttle range. I can get this thing to do ~50mph in current form, so I think some plug chops are in order to find where I'm too rich. Stay tuned...

Tugboat · « **Reply #28 on:** October 07, 2013, 09:42:17 AM »

Pulled the bowl off and looked at the slow jet. I tried to take a pic but my camera wouldn't focus that tight.. suffice it to say that what should have been a #38 looked like a damn main jet! Some PO probably cleaned it out with the smallest drill bit they had and now it's... maybe a #80? HUGE!! The main is a 110 (stock is 105). I have access to a Keyster kit which only had another 110 main, but it also had a #38 slow jet so I replaced that one. I also replaced the float, which turns out to be the same as on a CB350 and my buddies at Nashville Motorcycle Repair actually had one in stock. Put it all back together and took it out for some plug chops. Results:

Idle - at 2 turns out of the air screw

Mid

WOT - in 5th

I should have done WOT wound-out in 4th, since 5th gear is essentially useless. Not sure if it's the gearing or what but I can get up to about 55mph in 4th, but 5th doesn't seem to have any additional power. Also, WOT looks a little lean and it did help to give it a little choke.

It has a rattle too. Not sure if it's the top-end or what. I changed the oil this weekend and there were some non-ferrous fine metal flakes in it. Some small chunks in the oil pump screen too.

I tightened the cam chain while it was idling. Not sure if I tightened it enough, but I backed the tensioner all the way in/loose and then backed it out until I felt some tension. Might look at that again when I get home. Double-checked my timing while I had the oil drained out as well. Here it is on my way to work this morning.

DustyRags · « **Reply #29 on:** October 07, 2013, 12:58:10 PM »

Ah, the fine art of mangling jets! Good catch!

Bike looks nice.

Tugboat · « **Reply #30 on:** October 15, 2013, 09:19:01 AM »

Here it is with one of it's cousins at the Barber Vintage Fest in Birmingham, AL this past weekend. Ran great. Turns out the forks were twisted, but we loosened the triples and got it all back straight again. Picked up some clubmans that I might use (right-side up, of course), a new headlight bucket, front brake switch.. never did find side covers or a front fender.

Tugboat · « **Reply #31 on:** October 24, 2013, 09:55:43 AM »

Now with clubmans...

Finally got the carb tuned. I was running pretty lean at WOT with the #110 main. #105 is stock for this motor/carb setup. I figure the CB125 air box I'm running is less restrictive than the CB100 one. I've gone up in steps of 2.5 and finally settled on #117.5 - five steps up from stock. I started out getting about 52-53mph at WOT in 4th (5th is pretty much useless) and yesterday I got it up to 60mph with the proper jetting.. a 13% increase.

Next up: re-routing some cables, cutting and painting the fenders, new grips.

Also, I should note that I have a weird rattle. It changes with engine speed, and is the likely culprit for the aluminum sparkles in my oil. Probably a cam bearing failing? I need to open up the valve caps and make sure I'm getting oil up there. I have a whole new top-end I can swap over when/if it fails.

Tugboat · « **Reply #32 on:** October 02, 2014, 10:33:17 AM »

AHHHHHHH>>>>

Well, it's been a while since I've had time to mess with this thing. I've used that time to assemble some parts and finally got around to pulling the motor. Might I add that engine tear-down on one of these little things only took me & Spanner1 like an hour or so, and that was including trips to the beer fridge.

The good news: cam & journals actually look great. Normal wear, and no signs of oil starvation. Didn't get a pic of the journals but here's the cam.

I did, however, find the source of the ticking noise.

The cam chain must have gone un-adjusted for some time and got stretched out and started flopping up against the side of the case. The tunnel on the cylinder looks similar. It also damaged the cam sprocket.

I'd already bought a "new" head that's in good shape and its matching cam, and had new valves installed and the seats cut. Also have a new cylinder, piston, rings etc that I'll be installing.

I guess what I'm wondering now is what to do about whatever residual aluminum flakes that may still be down there in the bottom end. After my first oil flush, where I found the aluminum, I'd replaced the oil and ridden it around some. Again, pulling 60+ mph in an effort to get the carb jetting right. Also, this motor had undoubtably been run for some time while the damage was occurring, and by looking at the cam & journals it had never been enough of an issue to block any oil passages or cause any wear. Finally, when I drained the oil the other night prior to pulling the engine, I didn't see any metal in it. So should I just put it all back together & go for it? Flush the bottom end with oil or diesel or something?

grcamna2 · « **Reply #33 on:** October 02, 2014, 02:58:07 PM »

Nice CB112 Tug

Tugboat · « **Reply #34 on:** October 08, 2014, 08:34:06 AM »

Oil "filter"

When I drained the oil prior to tearing down the top end, I noticed that there wasn't nearly as much "sparkle" to it as there was the first time I drained the oil. Looks like the centrifugal "filter" is doing its job?

grcamna2 · « **Reply #35 on:** October 08, 2014, 07:38:11 PM »

Quite a few aluminum chips in that spinner/filter there Tug...

I think a few good changes of oil and clean the spinner out a few times with-in a 250 mile run-in should help.

News:

Author Topic: CB100/CB125 Hybrid aka CB112.5 (Read 8680 times)