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The Vintage Japanese Motorcycle Owners Group: Discussion Forums

Vintage Japanese Motorcycle Owners Group :: View topic - '73 CL100 fix-up


'73 CL100 fix-up
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spurlock
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Joined: Jul 08, 2014
Posts: 868
Location: Vacaville, CA

PostPosted: Fri Aug 18, 2017 3:55 pm    Post subject: Reply with quote

Sounds like you're making good progress. You can check the charging system performance with a voltmeter and ammeter. With a voltmeter across the battery terminals, with a fully charged battery, you should see 6.8 volts with headlight off at 1000 rpm, and 7.8 V at 5,000 rpm w/headlight on or off. With an ammeter in series with one of the battery terminals, you should see positive current flow start just above 1,000 rpm and increase to 1.3 amps at 5,000 rpm with headlight either on or off. Again, this assumes a fully charged battery. If you get similar figures your rectifier is good. Make sure the brake light switches are adjusted properly because if the brake light is continuously on the charging system will not keep up and ignition power will suffer.

-Bill

_________________
1975 Honda CB125S
1975 Honda XL250K2
1989 Honda NX250
1989 Honda GB500tt
1990 Honda GB500tt
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dgjessing
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Joined: Aug 11, 2017
Posts: 63
Location: Columbus, OH

PostPosted: Sat Aug 19, 2017 3:55 pm    Post subject: Reply with quote

Gotta get it running first Sad

I just discovered that the screw holding the point cam / spark advance unit in place on the cam shaft is sheared off, and the locating pin was rattling around in the recess. It appeared to be OK a few days ago, but I did not put a wrench on it, so I don't know if it was just hanging on by a thread (no pun intended) or if it broke off during the 40 second run the other day (or both). But this certainly explains why the timing was so far off compared to the picture in the manual.

So, fuck; you know? Hopefully I can coax the broken screw out of the cam shaft without any major surgery...
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spurlock
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PostPosted: Sat Aug 19, 2017 4:31 pm    Post subject: Reply with quote

Bummer. But that broken bolt should come out easily since it should not be bottomed in the hole. Have a left handed drill bit to try?

-Bill

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1975 Honda CB125S
1975 Honda XL250K2
1989 Honda NX250
1989 Honda GB500tt
1990 Honda GB500tt
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dgjessing
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Joined: Aug 11, 2017
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Location: Columbus, OH

PostPosted: Sun Aug 20, 2017 7:51 am    Post subject: Reply with quote

spurlock wrote:
Have a left handed drill bit to try?

-Bill


I'll run over to Harbor Freight tomorrow.
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dgjessing
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PostPosted: Sun Aug 20, 2017 3:46 pm    Post subject: Reply with quote

Made it over to HF today instead - that screw came right out with the bit just scratching the surface Very Happy

And, bypassing the wiring harness, I'm getting a nice fat spark now, so I know the points, condenser and coil are fine. Got a little more work on cleaning up the wiring; I predict it will be running tomorrow or the next day.

Oh, and the sister is back and the title is ready to be picked up!
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spurlock
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PostPosted: Sun Aug 20, 2017 4:13 pm    Post subject: Reply with quote

Good work! Besides cleaning/tightening wiring connections, it's worth pulling the backing plate off the key switch and cleaning the contacts. Carefully pry the round back switch cover from its plastic case, being very careful not to let the brass contact plate, spring and ball bearing fall out.

The kill switch is another potential source of resistance in the ignition circuit. You can just bypass it by connecting the black and black/white leads going to it.

-Bill

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1975 Honda CB125S
1975 Honda XL250K2
1989 Honda NX250
1989 Honda GB500tt
1990 Honda GB500tt
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mc67crew
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Joined: Nov 28, 2016
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PostPosted: Mon Aug 21, 2017 3:52 am    Post subject: Reply with quote

I can personally attest to the durability of the early 70's Honda 100cc engine.
My dad bought a near basket case CL100 for me to learn wrenching skills.
The previous owners kids had ridden this thing WFO all day,every day for years.
Never changed the oil,etc.
Those engines are so mildly tuned they won't blow up,if you keep oil to them.
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dgjessing
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PostPosted: Mon Aug 21, 2017 2:16 pm    Post subject: Reply with quote

Still no joy - weak spark, I think (again). Why are there two wires coming out of the condenser? I've never seen that before... With mine, there is continuity between the two.
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spurlock
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PostPosted: Mon Aug 21, 2017 4:20 pm    Post subject: Reply with quote

dgjessing wrote:
Still no joy - weak spark, I think (again). Why are there two wires coming out of the condenser? I've never seen that before... With mine, there is continuity between the two.


The two condenser leads join at the condenser, so they will show continuity, they are really the same wire. It's just a way to connect the points lead, coil lead and condenser using two connectors rather than three.

-Bill

_________________
1975 Honda CB125S
1975 Honda XL250K2
1989 Honda NX250
1989 Honda GB500tt
1990 Honda GB500tt


Last edited by spurlock on Mon Aug 21, 2017 4:24 pm; edited 1 time in total
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dgjessing
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PostPosted: Mon Aug 21, 2017 4:23 pm    Post subject: Reply with quote

That's what I thought - thanks for the confirmation! I'll try a new one tomorrow.
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dgjessing
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PostPosted: Tue Aug 22, 2017 2:10 pm    Post subject: Reply with quote

Success! After much dicking around I determined that my half-way decent spark was actually taking place near TDC on the exhaust stroke Embarassed In my defense, the manual clearly shows the points located on the top of the backing plate, not on the bottom where they need to be now. See the attached picture - it runs like this...

Is it possible to assemble the spark advance / point cam gizmo 180* off? I'll get in there and figure it out.

So anyway it now runs, but won't idle and likes being choked half-way. Getting the correct air filter will certainly help, and the idle jet needs to be adjusted. But it sounds good - no expensive noises or worrisome vibrations.

I'm pleased Very Happy [i]



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spurlock
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PostPosted: Tue Aug 22, 2017 2:21 pm    Post subject: Reply with quote

dgjessing wrote:
Success! After much dicking around I determined that my half-way decent spark was actually taking place near TDC on the exhaust stroke Embarassed In my defense, the manual clearly shows the points located on the top of the backing plate, not on the bottom where they need to be now. See the attached picture - it runs like this...

Is it possible to assemble the spark advance / point cam gizmo 180* off? I'll get in there and figure it out.

So anyway it now runs, but won't idle and likes being choked half-way. Getting the correct air filter will certainly help, and the idle jet needs to be adjusted. But it sounds good - no expensive noises or worrisome vibrations.

I'm pleased Very Happy [i]


Congratulations, but I'm laughing at the upside down points plate. Yep, you've already guessed the reason: the advance cam is put onto the advancer 180 deg. off. There is s slight notch on the cam and a half round cutout on the advancer base. Those should be on the same side.

IF it won't idle it's likely the idle jet is plugged. Very small openings in those and they clog easily.

-Bill

_________________
1975 Honda CB125S
1975 Honda XL250K2
1989 Honda NX250
1989 Honda GB500tt
1990 Honda GB500tt
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dgjessing
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Location: Columbus, OH

PostPosted: Tue Aug 22, 2017 4:18 pm    Post subject: Reply with quote

Alright, point cam thing fixed. For future reference, it's possible to fix it without completely dismantling it. I noticed this fact after completely dismantling it Rolling Eyes

The wide-open intake has got to be making it run way lean. I'll order a filter & a snorkel tonight. I imagine that tomorrow I won't be able to resist rigging something up to temporarily fix it well enough for a ride around the block. Duct tape? Wink
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spurlock
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PostPosted: Tue Aug 22, 2017 4:44 pm    Post subject: Reply with quote

I still suspect a problem with your idle circuit since the air filter and intake tube don't affect idle. Either that or there is an air leak between carb and engine. As for the half choke, the choke blade only affects mixture if it extends below the bottom of the throttle slide. So for example at half throttle the choke has to be lower than the slide to restrict intake air, otherwise it is above the air flow and cannot "choke" it.

-Bill

_________________
1975 Honda CB125S
1975 Honda XL250K2
1989 Honda NX250
1989 Honda GB500tt
1990 Honda GB500tt
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dgjessing
Weekend Warrior
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Joined: Aug 11, 2017
Posts: 63
Location: Columbus, OH

PostPosted: Wed Aug 23, 2017 5:01 pm    Post subject: Reply with quote

You are probably right about the dirty idle circuit - I wouldn't be surprised if a chunk of rust flaked out of the newly cleaned tank and made it through the iffy old filter. But it has started first kick a couple of times today so I'm optimistic!

I've got a bunch of necessary odds & ends on the way. Busy for the next week or so but I'll get back into it ASAP. Very Happy
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