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Author Topic: 1975 Honda CB125S  (Read 7178 times)

Offline crazypj

  • Posts: 13118
  • Split personality, I fake being smart
Re: 1975 Honda CB125S
« Reply #60 on: Aug 10, 2017, 21:47:44 »
It shouldn't be rich if float height is correct. Either shut off valve isn't sealing or float level is too low.
I pretty much always set float level +1mm when airbox is remved.
You should need about 10% larger main jet , pilot jet will be fine as original filter was virtually zero restriction at low engine speeds.
You will probably have to drop needle rather than raise it
I found some pictures of back light fitted but 'lost' them again   ::)
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline vwrabbit

  • Posts: 102
Re: 1975 Honda CB125S
« Reply #61 on: Aug 11, 2017, 10:19:53 »
I've checked float.  I think I finally have it set right.  At least I hope it's right.  I believe I have it set at 24mm.  I'll have to try a plug chop to see how its running.  It seems to be really, really rich at idle/no load revving.  I did also raise the needle one notch.  I'll drop it down 2, 1 below stock and see how that affects things.  I'll figure out carb tuning one of these days even if it kills me!   ;)

Offline crazypj

  • Posts: 13118
  • Split personality, I fake being smart
Re: 1975 Honda CB125S
« Reply #62 on: Aug 11, 2017, 11:30:30 »
At least carb is easy to get on and off and you only have one to worry about  ;)
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline vwrabbit

  • Posts: 102
Re: 1975 Honda CB125S
« Reply #63 on: Aug 14, 2017, 15:14:25 »
Too true!  My KZ440 is a PITA to do carb work on.

Offline vwrabbit

  • Posts: 102
Re: 1975 Honda CB125S
« Reply #64 on: Aug 21, 2017, 22:20:34 »
Pretty sure it's running lean. Moved the needle down one from stock. Runs better, but still stalls after it warms up. Need to go up a few sizes on the main jet. Pilot jet still good at stock size?

Offline crazypj

  • Posts: 13118
  • Split personality, I fake being smart
Re: 1975 Honda CB125S
« Reply #65 on: Aug 30, 2017, 21:19:36 »
The 75 should be good on pilot size, they didn't start getting stupid lean until 78~79. Check carb specs on a 74 to be sure though. You shouldn't need more than 15% larger than stock  unless you run no filter and short pipe (without any form of silencer or pipe extension)
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline vwrabbit

  • Posts: 102
Re: 1975 Honda CB125S
« Reply #66 on: Aug 30, 2017, 21:37:37 »
The needle jet is a 98. Stock says it should be 105. Pilot I think is a 38 if I remember correctly. Which is correct. Couldn't find this style jet anywhere on JetsRUs. About 34mm long, 8mm wide threads, 8mm nut. But it is a Kehin. It has the styled K on it. Cleaned the jets out some more and it helped a good bit. They must have not been fully clean and smooth. 

Offline crazypj

  • Posts: 13118
  • Split personality, I fake being smart
Re: 1975 Honda CB125S
« Reply #67 on: Aug 30, 2017, 22:08:40 »
Your probably looking at the jet still in the emulsion tube. Hold the 8mm hex and unscrew the jet out. May be stuck so look and feel like it's one piece.
I wouldn't have thought about it if you adn't mentioned some sizes, had the same issue when I was tying to make jet set up 'long distance' for someone  on here a few years ago. Went on for weeks mailing stuff back and forth until he mentioned something similar.
98 is main jet, needle jet will still be in carb body. It's a transitional size  with different needle, use 105 ~ 115,  may be lightly rich mid range but dropping needle should sort things out
« Last Edit: Aug 30, 2017, 22:16:08 by crazypj »
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0

Offline vwrabbit

  • Posts: 102
Re: 1975 Honda CB125S
« Reply #68 on: Aug 30, 2017, 22:29:28 »
Hmm. I'll take another look. Thanks for the info!

Carbs are fun, mmkay!

Offline crazypj

  • Posts: 13118
  • Split personality, I fake being smart
Re: 1975 Honda CB125S
« Reply #69 on: Aug 31, 2017, 13:16:55 »
Carbs are fun, mmkay!

They are when your watching someone else 'fix' them  ;)
 I still can't find pic of tail light on bike so I did a quick eBay for one
http://www.ebay.com/itm/Lucas-Style-Motorcycle-12V-LED-Tail-Light-For-Triumph-British-Cafe-Racer-Chrome-/262759607036?epid=2102678645&hash=item3d2db16afc:g:k28AAOSw6DtYTrBt&vxp=mtr
I particularly wanted bare alloy as it is more 'traditional' for a 60's style cafe. The prices haven't jumped too much since 2010
 
« Last Edit: Aug 31, 2017, 13:50:09 by crazypj »
'you can take my word for it or argue until you find out I'm right'
Best thing I ever overheard
"yep, PJ's my boss, he taught me everything I know, just didn't teach me everything he knows"
Brian Morgan, 1982

CB360's,  http://www.dotheton.com/forum/index.php?topic=11736.0
XS650,  http://www.dotheton.com/forum/index.php?topic=11922.0