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Project Bike SOTU 2017: Honda CL125S

IT LIVES! Having just come back from a cruise through my neighborhood, I can report with some excitement that my ’74 Honda CL125S is officially back on the road. Regular readers will recall from past Project Car SOTU articles that I bought this bike in April of 2014 in an attempt to recapture the sensations of my first motorcycle: a one-year-older CL125S that I bought in 1980 at the age of 17. Unfortunately, despite a healthy engine, this second trip down memory lane quickly turned out to be in unexpectedly sorry shape. I’ve had to do at least some work to nearly every component outside the engine cases, including a custom exhaust system.

My original intention to do a stock restoration was quickly abandoned because the original Honda parts were all either 1) impossible to find or, 2) obscenely expensive. The instruments, turn signals, switchgear, handlebar levers, and throttle have now been replaced with non-OE parts, removing from the rider’s view nearly all the vintage parts that reminded me of my first bike to start with. Unfortunately, the process was not as smooth as I hoped it would be. The six-volt electrical systems on small Honda motorbikes of that era are notoriously poor; after four decades of poorly executed patches and repairs by previous owners and the whole thing was a diagnostic quagmire.

Add in a mismatched selection of “universal fit” parts made in Indonesia, and things got unexpectedly complicated.

I haven’t ridden the bike hardly all since first getting it running two years ago. The only significant excursion, prior to my quick blast this morning, was a 20-mile shakedown run 14 months ago. That ride revealed a multitude of electrical and carburetion issues, thanks to years of neglect and some stupidly executed “fixes” by a previous owner. Also, the third used, replacement Honda speedometer I’d purchased lasted about a quarter mile before its insides exploded. I gave up and bought a generic chopper speedometer. Since the indicator lights were originally inside the speedometer housing, I also purchased a stand-alone idiot light panel originally from a Honda CB350 twin.

The biggest issue was an electrical problem that I just couldn’t figure out, despite tracing it down to the left-side handlebar switch unit. Since I also needed to replace the throttle twistgrip (Honda’s weird-alice, balky, internal-cable design), I bought all new switches, levers, and throttle off Ebay. The functions of the switch units didn’t match up exactly to the originals, and they had a few extra wires, so I spent time trying to figure it out. No matter what I did, I couldn’t get the headlight to work, even though both the expensive, proprietary sealed beam bulb and the handlebar switch were brand new and bench-tested perfectly. Since replacing the switch unit didn’t solve the problem, it had to be somewhere else, right? I literally spent hours repeatedly tracing wires all over the bike, looking for corroded connectors or frayed insulation that might explain the issue, with no luck. I also doubted my understanding of the circuitry; while seemingly simple, it’s rather non-intuitively configured.

After messing around with it in my free time over the course of several months, I finally concluded that I was just too stupid to fix it. I pushed the thing into a corner of the garage in defeat and left it there for most of 2017. Well, one Saturday morning last month I gave myself a pep talk and started over, troubleshooting from scratch. I then discovered the bizarre reality of the situation, as demonstrated in the hastily-recorded iPhone video below. It is so unlikely a scenario that I once I discovered it, I didn’t feel nearly so stupid.

The success of my deep-dive down the troubleshooting tree re-energized my efforts on this bike. I ordered a much higher quality universal switch pod, which—after more wire tracing and diagramming—turned into a fairly straightforward installation last weekend.

Meanwhile, I filled, charged, and installed a new 6-volt battery. Then, this morning before work, I hooked up the new throttle cable (actually intended for a TRX125 four-wheeler), rolled the bike out into the driveway, and give it a good kick. And another. And another. After kicking, then attempting to bump-start the bike, numerous times, it was clear that something was amiss. I pulled the spark plug and held it against the head as I kicked—no spark. Oh, crap, I had screwed up the wiring somewhere. Wait, I thought. The kill switch on this bike works by grounding out the coil (as I said, unintuitive). Could it be that easy? I switched the aftermarket kill switch to the “stop” position and give it another kick. My effort was met with a bright, blue spark. I reinstalled the spark plug and moments later the bike roared to life. I fiddled with the idle adjustment screw and soon she was ticking over evenly, something I had not been able to make happen with the old, sticky throttle and kinked cable. Damn, it’s good to be a wrench.

Having the bike on the road doesn’t mean its finished; not by a long shot. The fuel cap still weeps slightly, the rear brake is only marginally effective, and I need to play with the weight and volume of oil in the front forks. I might replace the somewhat dim turn signals with some better quality, bright units, because getting hit is bad. The bike still needs a lot of cosmetic work, such as paint, stripes, and reinstalling the tank and side cover emblems. So much time has past since I finished the exhaust system that I’ll need to buff off some surface rust before I can shoot it with high-temp flat black paint.

Spending time in the workshop also motivated me to get busy working on my “real” project, Bultakenstein. But that’s another SOTU article.

  • jeepjeff

    Oh man, that switch problem is evil.

  • Rover 1

    “he rear brake is only marginally effective” so it’s still stock then?

    The wiring is pretty easy to replace, there’s not much of it.

    But don’t do what my brother did with the rewire of his very similar SL125 and use only one colour of wiring. It makes newer faults hard to troubleshoot.

  • SlowJoeCrow

    Good work, your switch woes remind me of the moment of non-illumination when trying to get my 78 BMW R100S to start after a long time in storage. It would buzz and click but the starter wouldn’t engage. The voltmeter showed 13V on the battery terminals so I thought it was good until I put a test light across the terminals and watched the light go out after 5 seconds, indicating a sulfated battery with only a surface charge. This was after buying 2 new relays so I feel a bit foolish.