Topic: Auxilium fratribus (Help a brother out)

[Gman]

I have been banging my head on the wall for way too long.   
The bike:
1976 CB550K   20,533 miles as of today

Engine:
Stock airbox, stock carb internals with stock settings (clip position, jets, etc.) - all Keihin original brass. IMS screws 1.25 turns out.  Uni foam filter - properly cleaned and oiled.  Bought the bike with a 4-2 and last year replaced with MotoGPWerks 4-1 (had to lose centerstand).  Denso x22es-u plugs.  TEC points.

New/rebuilt/modded over last 5 years:
LED headlight.  Just replaced bars with 400 bars and new controls (main impetus for swap was the starter button was hashed on the old set and other internals were sketchy, etc.). Also just replaced stock pegs with rearsets mounted to passenger peg mounts.   New reg/rec.  One year old sealed battery w/battery tender.  LED rear turn signals/brake light, carbon fiber rear fender.  Rebuilt forks, rebuild front brakes/caliper, rebuilt master cylinder (moot point, as it's now an aftermarket mc to fit with 400 bars), new chain, new sprockets, cleaned/rebuilt carbs, converted to tapered steering bearings, new Frankenstuff side covers (painted black for simplicity at the mo), cleaned all terminals and added dielectric grease as I went, new o-rings in intake manifolds, new airbox to carb rubbers and carb to engine rubbers, rebuilt petcock.  New (last year) Dyna 5ohm coils, wires and NGK plug boots.  New condensers and points a few years ago.

Still to do: blast/paint/install Lesters (I actually have 2 sets w/CB550 specific rear), new tires, blast/paint/install gen-u-ine Dresda swingarm, install Hondaman transistor ignition (just got a month or so ago, but want to get it running properly first), fork brace (need to acquire, but already have '78 forks to replace shorter '76 forks so I can run fender AND fork brace), blast/paint/rebuild/install Marzocchi piggyback shocks (have 2 sets + rebuild kit), install CB650 cam and later model rocker cover with pinned shafts (have both, but want to get it running properly first), repaint sidecovers and spare tank.

Issue: Living in MN the riding season is already relatively short and with 2 kids, the time I can dedicate to the bike is further limited, although as they get older, I have more discretionary time.  Typically in the spring I do a 3K mile tune-up.  Tappets, points gap, timing, cam chain tension, carb sync, oil change, clean air filter, brake check, tires, etc.  About 2 or 3 years ago, the bike started running rough - fouling plug #1, which runs cooler compared to #2-4 (approx. 115 degF vs. approx. 150 degF). 

Bike idles easily, if rattly at 900 rpm and very happily at 1000 rpm.  Does NOT ever really need choke - not sure why.   With new/clean plugs, pulls hard to near redline, runs great.  After a few miles, starts stumbling a bit off idle and surging/mis-firing(?).  Gets worse as ride goes on.  On hard acceleration and upper rpm it smooths out, but overall just steadily gets worse (presumably as plug fouls).  Revs seem to drop easily/quickly and it still seems to idle pretty well even when running rough under load.  After ride plug #1 fouled (black, wet looking) is one issue and it feels like the bike is fighting itself (not sure if that's carb sync or fouled plug).

I've tried everything.  Read up on possible culprits ad nauseum.  Initial thought past couple years was it had to be carbs.  Re-cleaned carbs multiple times (spotless), messed with IMS screw settings, changing clip position on needles, re-timing, re-gapping points, re-syncing, cleaned emulsifier airhorn pipes per Hondaman (they were clean, but did it anyway).  This year thought maybe vacuum leak, hence new rubber.   Shakedown run today (after new rubber and sync) indicated otherwise, as same symptoms reared their ugly little rat-bastard heads.  Sorry; I digress.

I do enjoy taking on challenges, learning new things, and fixing/maintaining my own things, but I also like to ride.  I'm tired of chasing my tail and rather than wrench 5 times for every ride (and still not have it running right), I'm at the point where I would like a second opinion.  I'm open to someone above my pay grade coming up with something I didn't think to try or a forum member in Twin Cities metro who knows bikes that I can bribe/pay to help a brother out or someone with a recommendation for MN shop that knows these old CBs.

Peace,
G

[scottly]

Is the #1 plug the only one showing carbon fouling? If so, you have a problem with the #1 carb. Have you checked the fuel level in the float bowl using the "clear tube" test?

[Gman]

That's been my assumption all along, but I can't seem to find the smoking gun.

I did the clear tube method last summer (all good) and just had the carbs off yesterday to clean the emulsifier tube airhorn and I checked the #1 float manually (22 mm). 

I'll pull all the plugs tomorrow and try to upload some pics.

[ekpent]

 Lots of o-rings in those 550 carbs but sounds like you probably already have fresh ones in there. Does it have new o-rings under the cast exhaust manifold to the head ? I hope you can find the problem and get some good rides in. Summer is moving along quickly.

[bryanj]

Plug cap and/or connection to ht lead

[Gman]

Plug cap and/or connection to ht lead

I did give the plug cap a once over and it seems tight on lead.  Then I unplugged/re-plugged to coil to make sure that was good.  Maybe I'll swap #1 and #4 wires to see what happens.  Thx.

G

[Deltarider]

Plug cap and/or connection to ht lead

This ^. All CB500-CB550 owners should routinely check this and for intermittently (!) arcing between the lead and/or cap to the head. Once a sparkplug gets fouled, there's a chance it will not function properly afterwards anymore, not even after cleaning. This arcing is best detected in the dark. You can sometimes hear it crack. I take it the fuellines have the proper length of 17cm (to carbs 1+2) and 28cm (to carbs 3+4) and you have NO inline filters.

Bike idles easily, if rattly at 900 rpm and very happily at 1000 rpm.

This is quite normal. Personally I'd opt for an idle of 1100 rpm.

Does NOT ever really need choke - not sure why.

This could indicate it's too rich. Normally you need choke, be it for a short period of time. I'd adjust the air screws to 1¹/₂ turn out as prescribed by Honda. On these oldstyle carbs ¹/₄ of a turn can make a lot of difference. Are you sure the little O-ring around the main jet seals well?

With new/clean plugs, pulls hard to near redline, runs great.  After a few miles, starts stumbling a bit off idle and surging/mis-firing(?).

After a few miles of what? I mean does that include waiting at a traffic light where the idling will cause the #1 plug to foul even more?

[Gman]

This ^. All CB500-CB550 owners should routinely check this and for intermittently (!) arcing between the lead and/or cap to the head. Once a sparkplug gets fouled, there's a chance it will not function properly afterwards anymore, not even after cleaning. This arcing is best detected in the dark. You can sometimes hear it crack. I take it the fuellines have the proper length of 17cm (to carbs 1+2) and 28cm (to carbs 3+4) and you have NO inline filters.

Does the same, even with new plugs.  No inline filter and proper length fuel lines.

This could indicate it's too rich. Normally you need choke, be it for a short period of time. I'd adjust the air screws to 1¹/₂ turn out as prescribed by Honda. On these oldstyle carbs ¹/₄ of a turn can make a lot of difference.

You are correct - 1.5 turns is stock.  I think I had them set at that before, but two days ago when pulling/cleaning carb I double-checked all settings and reset them to 1.25 based on my superb memory of what they should be.    I will correct that today.

Are you sure the little O-ring around the main jet seals well?

Believe so - main jets push in and stay put, even before putting on leaf spring.

After a few miles of what? I mean does that include waiting at a traffic light where the idling will cause the #1 plug to foul even more?

Yes, although yesterday I think I was only stuck at two lights and flogged it the rest of the time trying to keep it above 5k rpm.

[Stev-o]

No choke is ever needed?  Sounds like carb could be super rich.  Can you confirm you have genuine Keihin jets?  Aftermarket carb kits can be impossible to tune  [been there]

[Gman]

No choke is ever needed?  Sounds like carb could be super rich.  Can you confirm you have genuine Keihin jets?  Aftermarket carb kits can be impossible to tune  [been there]

Pulled plugs today - will try to upload pics.  #1 - fouled.  #2 - nice tan.  #3 - bit black on one side, but tan on other.  Hmm.   #4 - Almost looks lean.

Choke on 3/4 just to get it started, then doesn't like it.  Once started I close it to the detente just before it is completely off.

Will pull carbs (again) to triple dog quadruple check the brass, settings, o-rings, etc. 

Appreciate everyone's time and thoughts.

Peace,
G

[Deltarider]

I do it with the carbs in situ. I can do it blindfolded. The allen key facilitates it. I'm doing it right now. Why I'm doing it? To shoot some pics for all those that are so eager to buy stuff they do not need. Below you have the pic of a float needle that has been passing gasoline for 136.000 kms. There-is-no-wear-at-all. Even when you feel with your nail where you see a slight discolorisation, there-is-not-even-a-beginning-of-a-rim. I have also added a pic of the float. Have a close look at the tang. The dot where the pin of the float needle rests, is minimal in depth, a 10^th of a mm at most. So, all of you, suppress your addiction to buy stuff, maybe thinking you're doing something good for your bike. And stop the nonsense of messing with the float heights. They-are-always-right, unless the PO has been a reader of this forum. Does this go for all models? Probably not. I have heard a Honda mechanic complain about some model Goldwings of that era. But as for the CB500/550s with the oldstyle carbs, these brass parts live forever. It was his experience already 30 years ago. It's alo my experience. Have a close look at my pics, enlarge them as much as you like and be convinced.

[Deltarider]

To check the slow jets, you need a magnifying glass. Checking cannot be done without one. Period. Without you may have the impression there's dirt in there, but this can well be a trompe l'oeil, caused by the small bore in combination with the limitations of the human eye. Vary the magnifying glass' distance between your eye and the jet for a good look. Patience, it can take some manoeuvring to get the right distance (and before you know it, you've lost it ). When the jet shows a perfect round hole like in the pic, it's OK. Believe me, you will recognise that perfect hole when it is there. No need to poke in there with E-strings -good Lord! - and what have you. If needed, a simple copper wire is all it takes. So far I have not detected any wear at my jets nor do I have any indication for it.

[scottly]

And stop the nonsense of messing with the float heights. They-are-always-right,

The spring loaded plunger in the needles can fail, causing the fuel level in the float bowls to be too high, especially when the float height is checked with the carb on it's side and the float tang just touching the plunger. If the carbs are turned upside down, so the weight of the floats is pressing on the plunger, you can see a drastic change in measured float height. The clear tube test will show the actual fuel level, and is the final say on float setting.
Plugged idle jets jets do not cause rich running, but the side holes in the emulsion tubes can, if plugged.

[alacrity]

@Deltarider.  Ok well I have sliced all my slow jets in half as indicated in your photo... and besides the enormous difficulty of getting them reinstalled, the bike wouldn’t run right. So I used a couple tubes of JB weld to fill everything up and that should do the trick...

😉

To check the slow jets, you need a magnifying glass. Checking cannot be done without one. Period. Without you may have the impression there's dirt in there, but this can well be a trompe l'oeil, caused by the small bore in combination with the limitations of the human eye.

[Deltarider]

As far as slow jets in PD carbs on K3 models, I tend to recommend a small 'maintenance dose' every tankfill of fuel additive or lamp oil (= kerosene). I have the feeling modern gasolines are less lubricous since lead was phased out. 

[Don R]

 My experience with a problem child resulted in finding drilled stock jets and PO manipulated float levels. The springs in the float valves were very soft, so much that it was difficult to tell when they were set correctly. I replaced them and had to adjust the float levels once again. Other issues that have haunted me were, bad plug caps and a bad new plug. The no choke to start thing might be a clue.
  I did have a K1 with a set of points that couldn't be set properly but that's another thing altogether. When I replaced them with other used points it cured the bike. After multiple carb cleanings and swaps.
  Good luck and I hope you can enjoy it again soon.

[Gman]

Thanks, all. 

Delta - I, too, can pull the jets with my eyes closed at this point.    I pulled the whole carb bank to give everything a thorough going over - I'll double check jets, emulsion tubes, etc. to make sure they are in spec and spotless and will do same with carb bodies.  I'll get there - but it's a perfect day for a ride and my bike is in pieces.   

Scottly - I did the clear tube last year and it correlated to the manual float heights, but once I get everything buttoned back up I'll do that again to verify. 

Don - Doesn't look like the jets have been buggered - I have some extras that I pulled from a different set of carbs that you can tell were messed up, so I think/hope I'm able to discern that mine appear unmolested.  TEC points (new as of a year or two ago and I don't put on a lot of miles), but will take a look and cover all my bases.  Thanks for the input. 

Be well,
G

[Gman]

Well, I may be on to something.  Since last post:
Pulled tank, drained to look for sediment and at filter.  All clean. 

Pulled carbs and cleaned the brass, checking once again for debris, signs of tampering, making sure they were Keihin, etc.  Only thing I found that might have been an issue is I thought the o-rings could use some love, as they seemed a little stiff when I pulled them to clean the brass.  So, ordered new o-rings and installed. 

Short aside: the O-Ring Store is amazing - every o-ring you would ever need, wicked cheap (IIRC on the order of $0.10 - $0.40 each for what I wanted), and they shipped 2 day for $6.99.  Think I spent a total of $12 or something ridiculous and got enough main jet, float bowl, float bowl drain, needle seat jet, etc. o-rings for 4 or 5 rebuilds. 

Pulled manifolds (which had new o-rings as of a few years ago).  They are still pliable and sealing.

Bench synced, buttoned all back up, double-checked/set valve lash, points, timing, cam chain tensioner, clear float fuel height, and carb synced.  I will say I think the carb sync wan't great - partially b/c my motion pro non-mercury gauges are are low on fluid and it sometimes separates in the columns, but more I think b/c the carbs just don't want to sync.  I ordered a new needle gauge synchronizer, so that should help the fine tuning for the next round.

And,... same problem as before. 

Here's the a-ha... Today I was poking around in my box of carb parts (some spare stuff I'm not sure where I got and one set of brass from a set of '75 carbs I picked up) and I started looking more carefully at the brass.  In total I have 3 full sets: 2 sets of Keihin (the one on my bike and the one from the spare carbs) and one set of aftermarket (Keyster, I think, b/c the needles were in a Keyster plastic bag).  So, in my bin I should have 4 Keihin of everything and 4 aftermarket of everything.  I started counting - all jets accounted for, but I opened up the Keyster bag and the 4 needles in there had numbers stamped on them.  Oops. They are Keihin.  The needles from the spare carbs were still in the carbs, so I pulled them just to verify and they, too, are Keihin.  Based on my astounding inductive reasoning, the needles in my bike are probably Keysters.    I cleaned up both Keihin sets and tomorrow will swap the ones on my bike.  Please, please, please Lord let this help.

[RAFster122s]

The little tubes in the throat of the carb lead to various air and fuel passages and need to be clear and spotless too. Your needles are the likely culprit, I definitely agree

[HondaMan]

I think you're onto something with those parts, would like to add one more thought: the Keyster needle jets (in the carb body) have bigger holes in them than the Keihins. You usually end up having to install the Keyster needle jets when installing their needles, or else the slides will not close. If you then go back to the Keihin needles with the needle jets still being Keyster, the result is: they don't turn off below 4000 RPM. So, see if you can find the Kehin needle jets while you have those apart?

Also: with the carbs being off so many times, another question: do the old clamps still tighten up well on the hoses at the carb ends? If not, you can reshape the flat portion of the screw-head-side of the clamps (and I add a washer, shaved off on each side with a grinder so it is almost rectangular) to increase the leverage a little more.

[Gman]

The little tubes in the throat of the carb lead to various air and fuel passages and need to be clear and spotless too. Your needles are the likely culprit, I definitely agree

Chased all the tubes already, so they should be good to go.

[Gman]

I think you're onto something with those parts, would like to add one more thought: the Keyster needle jets (in the carb body) have bigger holes in them than the Keihins. You usually end up having to install the Keyster needle jets when installing their needles, or else the slides will not close. If you then go back to the Keihin needles with the needle jets still being Keyster, the result is: they don't turn off below 4000 RPM. So, see if you can find the Kehin needle jets while you have those apart?

Also: with the carbs being off so many times, another question: do the old clamps still tighten up well on the hoses at the carb ends? If not, you can reshape the flat portion of the screw-head-side of the clamps (and I add a washer, shaved off on each side with a grinder so it is almost rectangular) to increase the leverage a little more.

Needle jets, meaning emulsion tubes?  I'll have to double check.  I have looked at all the emulsion tubes (in parts and in carbs) and none of them have markings.  In my research on the forum, I haven't been able to ascertain whether the Keihins are marked and/or how to differentiate.  I think my boots are all sealing, but I'll double-check those, too.  Thanks for the tip and the washer trick.

[scottly]

And,... same problem as before. 

Is the problem the same, as in the #1 plug fouls, and when replaced the bike runs well until it fouls again? If so, the needles should affect all 4 cylinders the same, and you still have a problem with the #1 carb.

[Gman]

And,... same problem as before. 

Is the problem the same, as in the #1 plug fouls, and when replaced the bike runs well until it fouls again? If so, the needles should affect all 4 cylinders the same, and you still have a problem with the #1 carb.

Yes and no.  After riding for 15ish minutes, bike developed a stumble that got worse the longer I rode (mostly at 0-1/8 throttle - indicating slow jet issues, correct?).  When I got home, I took the header temps and #1 was much cooler than the other 3.  I just walked away, so didn't pull plugs or anything yet - just needed a break from it.  Will pull plugs and swap needles, etc. now that I've had some time to recover. 

[Gman]

And the plot thickens.  Pulled the needle from #4 on the bike... yeah, it's a Keihin.  So, it looks like (barring any surprises when I check the rest of the needles) that all the brass is gen-yoo-ine.