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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
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Location: Vacaville, CA

PostPosted: Wed Aug 23, 2017 6:26 pm    Post subject: Reply with quote

I have no doubt you'll get it straightened out, you're on the case. Good luck!

-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: Sat Sep 02, 2017 12:43 pm    Post subject: Reply with quote

Back on this thing after a week off. Got the title in my name now, which helps a lot with motivation Smile. Replacement rear fender is here, and I've got it cleaned up and installed. I'm totally re-doing the wiring to the after-market tail light right now (what a mess!). I've got all sorts of little rubber parts on order from Partzilla (tank & seat mounts, parts to re-build the fuel petcock, etc.) which are supposed to be here today.
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dgjessing
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PostPosted: Sun Sep 03, 2017 2:54 pm    Post subject: Reply with quote

Progress! Now that I can mount the tank properly, and the fuel petcock no longer leaks, I took the thing outside for some extended run tests. Note that I also cleaned the carb again and installed a new in-line fuel filter, so I'm confident that's all in good order. I do NOT yet have the air filter connected up - waiting on the rubber boot thing to arrive from Thailand.

The carb I have does not appear to be the same one shown in the manual. It's a Keihin "PD" "009[B]RNF". After much fucking around with the idle mixture screw (located underneath, just before the mounting flange) I can now get it to idle! Smile This with the choke opened half-way. But it won't idle with the choke opened all the way. Indeed, It's hard to keep it running at all with the choke open.

I also got the correct air filter element, and it seems to me the thing is pretty restrictive. I think maybe there isn't much point in continuing with "tuning" until I've got that air filter boot installed.

Getting close though Smile
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spurlock
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PostPosted: Sun Sep 03, 2017 3:14 pm    Post subject: Reply with quote

dgjessing wrote:
Progress! Now that I can mount the tank properly, and the fuel petcock no longer leaks, I took the thing outside for some extended run tests. Note that I also cleaned the carb again and installed a new in-line fuel filter, so I'm confident that's all in good order. I do NOT yet have the air filter connected up - waiting on the rubber boot thing to arrive from Thailand.

The carb I have does not appear to be the same one shown in the manual. It's a Keihin "PD" "009[B]RNF". After much fucking around with the idle mixture screw (located underneath, just before the mounting flange) I can now get it to idle! Smile This with the choke opened half-way. But it won't idle with the choke opened all the way. Indeed, It's hard to keep it running at all with the choke open.

I also got the correct air filter element, and it seems to me the thing is pretty restrictive. I think maybe there isn't much point in continuing with "tuning" until I've got that air filter boot installed.

Getting close though Smile


Good progress. You are right about the carb - it's not stock. The original has an idle air screw at the air intake end. Yours apparently has an idle mixture screw (CCW is richer). So all bets are off on what correct jetting is. I think you are wise to wait for the intake tube before doing more carb work. Got a photo of the carb?

One thing that you could check now is the ignition advance if you have a strobe timing light. Make sure the F mark lines up at idle and that timing reaches full advance marks at higher rpm, around 3K. If it does not have pretty close to the full advance range, check to see if the springs are very loose and preventing the weights from returning fully to rest. You can squeeze the loops on the springs slightly if needed so the weights return all the way to rest, then reset static timing and recheck with the light. None of this has to do with your choke problem but is just something to get dialed in.

-Bill

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1975 Honda CB125S
1975 Honda XL250K2
1989 Honda NX250
1989 Honda GB500tt
1990 Honda GB500tt
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spurlock
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PostPosted: Sun Sep 03, 2017 3:19 pm    Post subject: Reply with quote

Don't recall if you have looked at this, but be sure to check for air leaks between carb and head. Make sure the front of the carb is flat (ears not bowed out), and that O-rings/gaskets are in good shape.

-Bill

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1989 Honda GB500tt
1990 Honda GB500tt
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dgjessing
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PostPosted: Sun Sep 03, 2017 4:19 pm    Post subject: Reply with quote

A couple pictures of the carb attached. The idle mixture screw is visible in the left side picture. Don't think there are any vacuum leaks, but I'll double-check that. Thanks much for your help!


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spurlock
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PostPosted: Sun Sep 03, 2017 6:51 pm    Post subject: Reply with quote

OK, that is definitely a later model carb and it really looks to me like a smaller size. If so it will have smaller jets which would account for the lean condition. Might be worth looking for a stock carb on ebay which will make everything easier and ensure original power and smoothness.

Also, unlike the original, that carb has a butterfly choke rather than a slide choke, so you are right that it will richen the mixture even at lower throttle openings.

-Bill

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1975 Honda XL250K2
1989 Honda NX250
1989 Honda GB500tt
1990 Honda GB500tt
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dgjessing
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PostPosted: Mon Sep 04, 2017 5:50 am    Post subject: Reply with quote

Are the ~$40 clones any good?
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spurlock
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PostPosted: Mon Sep 04, 2017 8:06 am    Post subject: Reply with quote

dgjessing wrote:
Are the ~$40 clones any good?


I'm not familiar with those, maybe someone else here can chime in. I was just guessing about your carb being smaller than stock based on its appearance. You could confirm by comparing the bore of the aluminum spacer block and the carb bore.

In case you come across a used CB/CL100 carb, here are specs for jetting etc. for the different models of carbs used:



-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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PostPosted: Mon Sep 04, 2017 9:13 am    Post subject: Reply with quote

Actually the carb outlet is a bit bigger than the block - 26mm versus 24mm (ID). The bottom edges of the slide have been crudely beveled a little for no apparent reason. I'm inclined to try one of the clones...
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dgjessing
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PostPosted: Thu Sep 07, 2017 3:43 pm    Post subject: Reply with quote

And the new clone carb is here already! It *appears* to be of good quality on the outside anyway. We'll find out if it works probably tomorrow. See that hole I'm pointing to with the pencil? Is there supposed to be a corresponding hole in the intake block on the cylinder?


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spurlock
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PostPosted: Thu Sep 07, 2017 3:45 pm    Post subject: Reply with quote

dgjessing wrote:
And the new clone carb is here already! It *appears* to be of good quality on the outside anyway. We'll find out if it works probably tomorrow. See that hole I'm pointing to with the pencil? Is there supposed to be a corresponding hole in the intake block on the cylinder?


No, no corresponding hole in the intake block. Most likely that hole is plugged back in the carb a short distance.

-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: Thu Sep 07, 2017 3:48 pm    Post subject: Reply with quote

spurlock wrote:

No, no corresponding hole in the intake block. Most likely that hole is plugged back in the carb a short distance.

-Bill


Cool - that's what I figured Smile
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dgjessing
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PostPosted: Thu Sep 07, 2017 5:06 pm    Post subject: Tires Reply with quote

I've been having a hard time locating a 2.5" x 18" front tire on the internets. Any suggestions?

The correct tire sizes are 3 x 18 rear, 2.5 x 18 front. I've now got a 3.5 x 18 on the rear and a 3 x 18 on the front. As a result, the rear tire is in contact with the ground when it's on the center stand, and on the side stand it leans over at a ridiculous angle.

The existing rear tire is shot, but the front is in fine shape and only 5 years old. The plan is to swap the front to the back and get a new front.
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spurlock
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PostPosted: Thu Sep 07, 2017 5:58 pm    Post subject: Reply with quote

Yeah, it's getting to be slim pickin's on those smaller size tires. If you're wanting mainly a street tire this one is good:
IRC NR53 2.50-18

Or there is this more universal tread for a slightly more gravel road friendly style:
IRC NR2 2.50-18

-Bill

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