Author Topic: 550K1 - carb questions (022A)  (Read 6574 times)

Offline Erny

  • CB750K7 CB550K1
  • SOHC Pro
  • Posts: 522
    • View Profile
Re: 550K1 - carb questions (022A)
« Reply #30 on: June 27, 2019, 06:45:53 PM »
Currently no1 and 4 are 1.5 turn, 2 is 1.75 and 3 is around 1.6. I did that based on plugs colour, where 2 was darkest, 3 was bit dark, 1 and 4 I considered ok.
Attached how plugs looked like on Mon after I had all screws 1.5 turn and before longer riding (after that I found no3 bit too dark too) and before syncing carbs. I don't jave actual view, will take pic once I'll be back at garage.
CB750K7 US model (1977)
CB550K1 US model (1975)

Online K2-K6

  • Grogu
  • *
  • Posts: 5208
    • View Profile
Re: 550K1 - carb questions (022A)
« Reply #31 on: June 27, 2019, 07:34:51 PM »
Plug colour is usually main jetting accuracy,  and completed under load when fully up to temperature. You'd not normally trim with colour by using idle adjustments.

For plug "chop" you'd get it warm,  then ride it under full load with throttle wide open,  cut ignition,  then look at plugs.  It's setting the maximum demand mixture so that it's safely in correct range and not too lean that it will cause any damage. It's done like this to deliberately get the engine running fully on main jet and not influenced by low speed settings.

Idle air screws should be adjusted at tickover by bringing the engine speed to its highest level for each carb,  indicating that the slow speed mixture is correct. Honda manuals contain a routine for this.
If you get one carb not responding to this within a small range of the others,  then it indicates a problem with that carb.

Offline Erny

  • CB750K7 CB550K1
  • SOHC Pro
  • Posts: 522
    • View Profile
Re: 550K1 - carb questions (022A)
« Reply #32 on: June 28, 2019, 02:15:25 PM »
Yes I know about prcedure to tune slow. Despite I'm now quite skeptic, I'll try to still play with air screws hoping for improvement
CB750K7 US model (1977)
CB550K1 US model (1975)

Offline Erny

  • CB750K7 CB550K1
  • SOHC Pro
  • Posts: 522
    • View Profile
Re: 550K1 - carb questions (022A)
« Reply #33 on: June 28, 2019, 07:22:06 PM »
So, I tried to play with air screws, seems settings 1.5turn is the best... Strange.
Attached pic of plugs, no change 2nd still much darker
CB750K7 US model (1977)
CB550K1 US model (1975)

Online K2-K6

  • Grogu
  • *
  • Posts: 5208
    • View Profile
Re: 550K1 - carb questions (022A)
« Reply #34 on: June 28, 2019, 07:48:16 PM »
It's worth considering if no2 carb is operating the fuel level the same as the other 3.

Although set up correctly with float height dry checking,  some examples on here have shown different fuel levels when checked with a tube to show real time fuel level when installed on the bike.

Offline Erny

  • CB750K7 CB550K1
  • SOHC Pro
  • Posts: 522
    • View Profile
Re: 550K1 - carb questions (022A)
« Reply #35 on: June 28, 2019, 07:55:16 PM »
When I had carbs on the bench I did float height set to 22mm and then after closing bowls also with clear tubes, all were the same level. True is that after I did not test on engine. I hate that somehow as there is always gasoline on the engine, but will have to do.

Question is if one carb can cause behavior I'm experiencing?
CB750K7 US model (1977)
CB550K1 US model (1975)

Online K2-K6

  • Grogu
  • *
  • Posts: 5208
    • View Profile
Re: 550K1 - carb questions (022A)
« Reply #36 on: June 28, 2019, 08:07:37 PM »
You seem to have reasonably checked the things that affect it so it's a puzzle to see what is making that difference.

You are getting into a level that would be helpful to have more information to assist you in making decisions.  If it's running on four exhaust pipes you can get emmisions readings for each one to see how each cylinder is burning. HC level increase shows unburnt fuel (too rich)  so it would give you confirmation if you have access to test equipment.

Edit:- this thread recently looked into it like above http://www.sohc.co.uk/index.php/topic,18831.0.html

May be of interest.
« Last Edit: June 28, 2019, 08:26:10 PM by K2-K6 »

Offline Erny

  • CB750K7 CB550K1
  • SOHC Pro
  • Posts: 522
    • View Profile
Re: 550K1 - carb questions (022A)
« Reply #37 on: June 28, 2019, 11:24:44 PM »
Interesting!
I have original, 4 into 4 pipes.

Testing HC is definitely good idea, but I don't have access to, need to investigate...

But thinking more about it, my pipes are far from being perfect, all have small holes in lower seam and no1 and no4 (upper ones) have quite big holes on the bottom behind rubbers crossconnecting pipes at their back, see pics.

Can this cause my issue?

Pics of pipes and bike as it looks like attached
CB750K7 US model (1977)
CB550K1 US model (1975)

Offline Erny

  • CB750K7 CB550K1
  • SOHC Pro
  • Posts: 522
    • View Profile
Re: 550K1 - carb questions (022A)
« Reply #38 on: July 31, 2019, 10:05:43 AM »
Update on this issue.

Since last update I did:
- replaced main jets O-rings by proper ones 3.5x1.2 (bought in local shop). O-rings I had in carbs before were smaller crossection and larger diam and main jets were quite loose in casting. I had to apply some force to push jets into castings, before they went in very easy almost zero force. I was hoping that this is main reason for my issue (leak arounf main jets O-rings). Pic showing differences between O-rings attached
- replaced O-rings under intake manifolds (OEM). Another issue with manifolds discovered see another thread http://www.sohc.co.uk/index.php/topic,19713.msg174773.html#msg174773
- replaced rubbers between manifolds and carbs by new OEM
- carbs again checked for float height, including clear tube test (see pic for levels)
- carbs sync'ed after full warm up
- idle screws left in basic settings (1.5 turn)

Result:
There is zero or little improvement compare to before... Still, under ~3k RPM, using little trottle when trying to keep stable speed (cruising in the city) or trying to accelerate from ~2k - 3k still not good, engine has "hard" run, I feel it like too rich mix or like one cyl is not working. Otherwise, on higher RPM (5k+) I think bike runs well

I did >60miles test, most of the time bike runs on higher RPMs (this is my favourite test route, curvy uphill/downhill area). After i came back I check plugs. Result the same as before no2 is fouled, see pic. it is dry black smoke, easy to clean with brakecleaner, not oily. I can definitely put plug issue out of the question, becase I swapped plug 1 & 2 before this test, so previously dark no2 became clean in no1 and previously clean no1 is now black in no2..

Was thinking if this could be caused by coil/spark issue on no2 (intermittent spark, HT cable broken etc)?
But looking at plug there is some spark for sure. I tried to swap cables 2&3 but no2 is not long enough to reach cyl3...

Can somedy advice what else I can try/test?

note: Maybe no2 dark plug issue is linked to issues on low RPMs? (e.g. engine running virtually on 3 cylinders?)


CB750K7 US model (1977)
CB550K1 US model (1975)

Online K2-K6

  • Grogu
  • *
  • Posts: 5208
    • View Profile
Re: 550K1 - carb questions (022A)
« Reply #39 on: July 31, 2019, 10:51:11 AM »
To answer you're question about if the exhaust pipe hole could cause this problem,  I don't think that would because it's right at the end.

Have you considered moving the idle jets from one carb to swap with another to see if the problem transfers with those parts? Swap both jet and screw together to test it.

If it moves the problem,  then obvious which part is causing it. 

If it stays there as it is now,  then more linked to that cylinder.

To get one cylinder rich is less likely to be that cylinder specifically as it just needs more fuel to go like that.  Generally a fault mechanically would move toward lean.

So more likely fault is in the carb,  see what results you get with jet swap first as it may give definitive results.

Offline Erny

  • CB750K7 CB550K1
  • SOHC Pro
  • Posts: 522
    • View Profile
Re: 550K1 - carb questions (022A)
« Reply #40 on: July 31, 2019, 11:13:46 AM »
OK, I can try. This could be manageable w/o taking carbs off the bike.
I doubt this is caused by idle jets themselves as I replaced all 4 by new Keihin genuine (38). But screw is another story.

Back to my previous question - what about eventual issue with coil / HT lead? (plug caps are new, but I can swap no2 and 3 caps at least to exclude them from investigation)
« Last Edit: July 31, 2019, 11:17:37 AM by Erny »
CB750K7 US model (1977)
CB550K1 US model (1975)

Online K2-K6

  • Grogu
  • *
  • Posts: 5208
    • View Profile
Re: 550K1 - carb questions (022A)
« Reply #41 on: July 31, 2019, 11:23:54 AM »
Yes to swapping the plug cap,  but do each swap on its own to avoid confusion.

Offline Nurse Julie

  • 1977 CB550/4 Mongrel Brat. 1974 UK 500/4 K1. Honda CD250u.
  • Grogu
  • *
  • Posts: 8193
    • View Profile
Re: 550K1 - carb questions (022A)
« Reply #42 on: July 31, 2019, 11:42:46 AM »
You probably have but, have you checked that all the holes are clean and clear in the air screws?
LINK TO MY EBAY PAGE. As many of you know already, I give 10% discount and do post at cost to forum members if you PM me direct.
https://www.ebay.co.uk/sch/julies9731/m.html?item=165142672569&rt=nc&_trksid=p2047675.m3561.l2562

LINK TO MY CB400/4 ENGINE STRIP / ASSESSMENT AND REBUILD...NOW COMPLETE
http://www.sohc.co.uk/index.php/topic,14049.msg112691/topicseen.html#new

Offline Erny

  • CB750K7 CB550K1
  • SOHC Pro
  • Posts: 522
    • View Profile
Re: 550K1 - carb questions (022A)
« Reply #43 on: July 31, 2019, 11:47:32 AM »
Well, this I did not check honestly!
I assumed it must be clear as carbs came from Gerben completely dry, I used them first time after rebuild

But will check! Thanks!
CB750K7 US model (1977)
CB550K1 US model (1975)

Offline Erny

  • CB750K7 CB550K1
  • SOHC Pro
  • Posts: 522
    • View Profile
Re: 550K1 - carb questions (022A)
« Reply #44 on: August 02, 2019, 11:12:01 AM »
Small update : yesterday did test swapping plug caps no2 and no3 and cleaned plugs. Result is no change, no2 still dark.

Next steps
 - I'll try to test with another coil 2-3 to eliminate coil no2 output (cable) issue
- replace intake manifold 1-2 to ensure rubber seals as it should
- recheck carb2 for dirt, especially around airscrew
CB750K7 US model (1977)
CB550K1 US model (1975)

 

SimplePortal 2.3.5 © 2008-2012, SimplePortal