Topic: 1975 CB125 - little aluminum flakes coming out of the crankcase vent w/oily mist

[sangyo soichiro]

So... I happened to find a 17T drive sprocket tonight, put it on, and went for a spin.  I figured from a rough calculation that I should bump the max speed from 65 to 72.  But the darn bike didn't have the power to get up there.  In fact, I don't think it even got to 65.
Bummer.

[Flying J]

Sounds like you need a big bore. 

[crazypj]

You'll have to red-line it in 3rd before changing up it will probably be faster in 4th than in 5th without engine mods to pull the higher gear
You only have around 8~9 bhp to play with

[Flying J]

Plus mine had a cafe seat and clip ons. Thats good for at least 3 hp

[sangyo soichiro]

Plus mine had a cafe seat and clip ons. Thats good for at least 3 hp

 

Mine will have the standard seat, but I will have drag bars.   

Oh... and in case anyone is wondering how the heck I can be test riding a 17 tooth sprocket while still putting the engine back together, it's because I have two CB125's.   
(Well ok... one is technically my girlfriend's.) 

[sangyo soichiro]

Another question:
So I got the rings yesterday, and I notice the two top rings are slightly different.  One appears to be completely black-ish in color, but the other one appears to have a gray-ish colored ring on the outside surface that would be in contact with the cylinder wall (the oil ring also has this).  My question is: Which of these two rings goes where?  That is, does the all black ring go in the top spot of the piston, or does the one with the gray-ish outer ring go in the top spot?


See the attached picture for what I'm talking about.  You can see in the photo that the ring at the top of the photo is all black, but the ring at the bottom of the photo appears to have a gray-ish outer surface (as does the oil ring). 

[raymond10078]

Does this help?

[sangyo soichiro]

Does this help?

Indeed it does.  Thank you!

[raymond10078]

That excerpt is from the Honda Common Service Manual.

http://www.vf750fd.com/vf750f/Honda_Common_Service_Manual.pdf

[sangyo soichiro]

Wow!  Thanks very much for that link!  I didn't have that manual, but I do now, thanks to you.   

[sangyo soichiro]

Got her back together last night and she fired up.  Pretty happy about that.  Still some tuning to do, but so far so good.

[sangyo soichiro]

She seems to be tuned now, at least somewhat close to where she needs to be.  The P.O. put a pod filter on her, and I upped the jet size, but I think I need to play with that a little more.

She turned out to be a really nice little bike. I rode her around for a short trip close to home (walking distance, in case anything happened) last night.  I fixed everything on her including the turn signals and horn.  I put fork oil in (she was empty), and mounted drag bars on her for a little different look and feel.  I used the mirrors from one of my 750 parts bikes, and they look halfway decent on her.  I'll post a photo of her soon.

I named her Holly.  If it sounds ok, I usually name my bikes after the town that I got them from.  I got her from Holland Michigan.   

[Flying J]

Very good .  I usually name mine after the person who sold it to me.
My 125 ran great on a uni foam filter with no jetting change.

[sangyo soichiro]

Very good .  I usually name mine after the person who sold it to me.
My 125 ran great on a uni foam filter with no jetting change.

That's odd... the P.O. had a Uni foam filter on it but it didn't run quite right.  I had a spare 110 jet (there was a 98 already in it), and that helped a bit, but it may be a little rich now.  The problem I had was that I couldn't get it to idle.  I know the main jet shouldn't affect the idle, but in this case it seemed to help, for whatever reason.  And it runs ok at high speed, although bogs down ever so slightly if I completely open the throttle, which makes me think the 110 is a little too rich now.  I'm thinking about getting a K&N filter for it and a few smaller jets to help fine tune it.

I dinked with the ignition timing and the air screw, but I had a hard time getting it to idle without dying.  And it still doesn't purr like my girlfriend's stock 125.  Any tips?

[crazypj]

Drop the needle a clip,it could lean things out slightly also adjust float level +1mm higher than stock

[sangyo soichiro]

Drop the needle a clip,it could lean things out slightly also adjust float level +1mm higher than stock

Thanks for the tips.  I'll try that.   

[Flying J]

Sounds like your heading in the right direction with the tuning. I would go do a Plug chop for the main before i moved the needle. Its not hard to do a WOT plug chop on these bikes because they are so slow. Once you think you have the right main then do the slide. Thats the textbook way to do it i guess.

[sangyo soichiro]

Still messing with getting the proper main jet, but this is her.  She runs pretty well and seems to idle nicely now.  The seat has been taped over a rip, but I'm not sure I will replace the seat cover.  Maybe this'll just be my fun bike and not worry too much about looks.  Yes... that's one of those cheap Emgo air filters, but I had it on hand, and it seems to run ok with it on for now.