Topic: 550K0 Tuning Frustrations - warning: lots of details

[Jay D.]

1974 CB550K0

I have put so much work into this project and I feel that I have hit a wall.  However, I named my project "Wisdom and Patience" because I want to learn from this process and avoid making mistakes.

I have searched extensively and found bits and pieces that have helped.  However, I am feeling a little lost at the moment and appreciate any insight.

Here are the basics to help eliminate obvious issues:
-carbs thoroughly cleaned and rebuilt.  Manifold and airbox rubbers are in top condition with no signs of leakage.  Carb rack mounted nice and tight, no signs of leakage after multiple spray tests.  Rebuilt with full Keyster kit - I believe pilot 38, main 100.  (will verify ASAP)  Removed the rack again last week to make sure nothing was clogged, good seals, correct float levels.
-adjusted choke valves to ensure even seal and movement
-bench sync'd
-re-installed and ensured tight seal @ manifold, airbox, filter, etc.  Air connections between carbs also in fine condition.
-fresh clean fuel
-spark plugs clean and gapped - good spark from new NGK components
-valves adjusted
-timing adjusted - first static, then strobe
-cam chain adjusted
-carbs vacuum sync'd - very limited deviation between carbs
-exhaust collars snug with new copper gaskets
-throttle cables adjusted within spec
-idle thumb screw adjusted +/- throughout the process


So, generally speaking I can get the bike to sit nicely at idle.  I was even able to take her around the block a couple times last week.  However, sometimes the revs climb and climb and eventually sit again.  This is usually caused by a quick blip of the throttle but sometimes the revs climb when the bike is started (warm). 

The item I am currently addressing is the exhaust connection between the stock header and the brand new aftermarket MAC 4-2 exhaust. (The bike came with a hideous set of aftermarket exhaust - turned out slashed tips).  I had not yet sealed the connection and finally did so today.  I want to let it cure for 24 hours to see if this helped at all.

So, my question - is it possible that the leaking exhaust connection could have been affecting back pressure enough to mess with the vacuum?

If not, all other suggestions are welcome.

Thanks!

[kslrr]

Idle not setling in quickly and/or climbing like that is usually a sign of a vacuum leak (though it sounds like you have tested for that) or lean condition.  What is the condition of the fuel tank and in-line (if any) filter?

Also, I'd check the condition of the brass parts from the Kester kit sooner than usuall.  Kester uses soft brass.  I used Kester jet needles in my CB650; they were deteriorated 6 months later.

[swan]

Jay D,

I just went through many, many hours of frustration and finally solved the same idle problem on my 1975 CB400f. I tried everything you did and more. http://www.dotheton.com/forum/index.php?topic=39976.msg477564#new

You are experiencing "idle hang", (Goggle it with "Honda CB" and you will learn you are not alone). I solved it by using OEM Honda carb parts instead of aftermarket parts. I found through research and experience that the aftermarket part are not the same as OEM and cause both air leaks and and too rich of an idle. The main problem is the aftermarket needles do not seat well with the original carb emulsion tubes, allowing too much fuel to pass, enrichening the mixture and causing a temporary high idle. The rich and high idle fouls the plugs and then you drop down to normal idle rpms, but it never idles as smooth as it could or should. I switched back to the original OEM needles and eliminated this problem. I also found the diameter of the aftermarket air screws are slightly smaller, possibly causing air leaks. The only silver lining in this is everything else on your bike is now correct as you worked through this. Do you still have the original needles? If so, try them if they are not too worn. If not, "needle jet sets" are available as matched pairs from Honda (you will need 4 sets).

Good luck and post your results.

[matt mattison]

Is the idle speed adjustable with the brass knob when warm?

[Jay D.]

What is the condition of the fuel tank and in-line (if any) filter?
Also, I'd check the condition of the brass parts from the Kester kit sooner than usuall.  Kester uses soft brass.  I used Kester jet needles in my CB650; they were deteriorated 6 months later.

Fuel tank is in very good condition, no rust.  Brand new fuel lines.  No filter (yet) but I have checked the float bowls (drain and removal) and no signs of junk. 
Thank you.  I will take into consideration along with swan's suggestion.

I solved it by using OEM Honda carb parts instead of aftermarket parts.
Good luck and post your results.

Thanks for this insight.  I'll check out your dtt link. 
Yes, I kept all OEM parts.  I think I know the answer to this but will I have to go back to ALL OEM hard parts?  I suppose I wouldn't want to mix the OEM needles with the Keyster emulsion tubes, etc?  What about the float holder and valve?  Would be awesome if I didn't have to wrestle the darn rack out again but I think I know what you're going to say... 

Is the idle speed adjustable with the brass knob when warm?

I assume you are referring to the idle knob on the carb rack near #4?  Mine is not brass so I want to clarify.  If same, yes I am able to adjust idle easily with the knob.  Helps get it to sit at 1k but does not help the climbing and racing.

[swan]

The brass idle adjuster is irrelevant to this issue, it is in the idle circuit itself.  As noted, add an inline filter before you do anything else. They are cheap and effective.

Yup, you need to pull the carbs (again... You should be good at it by now. Use a strap to pull back and hold the air manifold). If you have the OEM carb parts try just the original needle and air screw, the float seat and valves are generally usable. Your emulsion tube should be original because I believe most aftermarket kits do not include them. Carefully press/push/pull out the tubes and carefully clean the tubes with a tiny strand of copper wire and carb cleaner (as seen in my build thread). Do not enlarge or alter the holes. Clean the passage that holds the tube and carefully push the cleaned tube back in place with a small diameter wood or soft metal drift. You do not want to mar or alter either end of the tube for it will affect fuel delivery. reassemble and this should help. As mentioned the metal used for the after market is quite soft and fails quickly. I paid $70 for four matched sets of needle jet sets (emulsion tubes and needle) from Honda Parts Direct. Worth the price after all the frustration and time. Also, use high octane, non-ethanol or oxygenated gas if possible. These motors were designed to run on real gas.

[matt mattison]

The brass idle adjuster is irrelevant to this issue, it is in the idle circuit itself.  As noted, add an inline filter before you do anything else. They are cheap and effective.

Yup, you need to pull the carbs (again... You should be good at it by now. Use a strap to pull back and hold the air manifold). If you have the OEM carb parts try just the original needle and air screw, the float seat and valves are generally usable. Your emulsion tube should be original because I believe most aftermarket kits do not include them. Carefully press/push/pull out the tubes and carefully clean the tubes with a tiny strand of copper wire and carb cleaner (as seen in my build thread). Do not enlarge or alter the holes. Clean the passage that holds the tube and carefully push the cleaned tube back in place with a small diameter wood or soft metal drift. You do not want to mar or alter either end of the tube for it will affect fuel delivery. reassemble and this should help. As mentioned the metal used for the after market is quite soft and fails quickly. I paid $70 for four matched sets of needle jet sets (emulsion tubes and needle) from Honda Parts Direct. Worth the price after all the frustration and time. Also, use high octane, non-ethanol or oxygenated gas if possible. These motors were designed to run on real gas.

The idle speed adjustment screw is quite relevant if the throttle slides were not set on the floor of the carbs on initial set up. As you know, when the bike warms up, the idle speed goes up a bit as well. When the linkage is set up this way, you can't drop the idle back down where it belongs via the adjustment screw . If he has full adjustment, then yes, the adjustment screw is irrelevant at this time. I just wanted to throw that out there before the carbs were taken apart again. Don't ask me how I know this

[Jay D.]

The idle speed adjustment screw is quite relevant if the throttle slides were not set on the floor of the carbs on initial set up. As you know, when the bike warms up, the idle speed goes up a bit as well. When the linkage is set up this way, you can't drop the idle back down where it belongs via the adjustment screw . If he has full adjustment, then yes, the adjustment screw is irrelevant at this time. I just wanted to throw that out there before the carbs were taken apart again. Don't ask me how I know this

I had the cabs apart last week hunting for issues. At that time I bench sync'd and set the throttle slides at the floor.  Idle adjustment has not been as issue thus far.  She will sit just fine at 1k and I can tweak up and down. It's the darnedest thing when I blip and revs climb. It's a little scary, too, because you think it's going to keep climbing and climbing. Sounds awful.

I just pulled the OEM bits from storage and snapped a couple pics. Will post in a bit to make sure I am staying on right track.

[matt mattison]

Like others had stated, could be the aftermarket parts. Seems as if you are pretty thorough. I assumed you already checked for the cables for binding .

[Jay D.]

Ok, just want to go over a few details before I continue.  I was so tempted to fire up the bike again this evening JUST to be able to say that the exhaust leak wasn't a culprit but I decided to wait and let the seal form until tomorrow night.

In the meantime, here are some of the OEM parts.  I left the float valve and seat out of the picture because I am going to proceed with the aftermarket set as noted and confirmed above. 

(for my own confirmation and peace of mind)
The needles are in upper right with air screws to their left, dark in color.
Bottom four barrels are the main jets (#100) and the four on left are the slow jets (#38).

I am embarrassed to admit that I do not think I pulled the emulsion tubes when overhauling the carbs.  Therefore it's likely that they are still full of varnish and would certainly not function properly with the Keyster needles.  Regardless, I plan on using the OEM needles and air screws after thorough cleaning.

So, a recap before I start working on this.  Please take a moment to confirm, @swan.
-Clean OEM components per your instructions
-Replace aftermarket needles with originals (I believe clips should be set @ second groove from bottom?  Will search again to confirm if you do not)
-Pull emulsion tubes, clean tubes and passages thoroughly and carefully
-Swap aftermarket air screws for OEM
-Ok to leave aftermarket main jets? (OEM can be cleaned up but looks like I marred exterior of one on left a bit when removing.
-Ok to leave aftermarket slow jets?

[Jay D.]

As noted, add an inline filter before you do anything else. They are cheap and effective.
Also, use high octane, non-ethanol or oxygenated gas if possible. These motors were designed to run on real gas.

Yes, I plan on ordering inline filters this week.  Is there a preferred brand?  (will also search forum)  I've seen a lot from a couple bucks on up.  Price isn't an issue, really, just want to make sure I don't overspend or buy crap. 

I've heard mixed things about fuel selection. I was under the impression that 87octane was considered the proper fuel for these old bikes?  87 is regular on the East Coast whereas I know some places out west 85 is regular .  I use 93 in my SV650 but have been testing this bike with fresh 87.  If I recall all the fuel around here is 10% ethanol.  Will have to confirm.

[phil71]

Did you replace the parts labeled #38 in this pic? If you didn't, you missed a notorious source of vacuum leaks on the 500/550

[Jay D.]

Did you replace the parts labeled #38 in this pic? If you didn't, you missed a notorious source of vacuum leaks on the 500/550

Negative.  With the carb rack off this week I'll certainly be checking them out now that you've brought them to my attention.  I will order a new set if they look anything less than stellar.  Thanks for the heads up!

[phil71]

 they are just o-rings..  30.8MM (which likely means they used an SAE o-ring)  can prob source them locally. I guarantee they are hard as rocks and flattened .

[Jay D.]

they are just o-rings..  30.8MM (which likely means they used an SAE o-ring)  can prob source them locally. I guarantee they are hard as rocks and flattened .

Just looked a spare manifold I have - yep, they're flat and hard. Would be nice to source locally but wasn't sure if req'd specific rubber compound due to heat?

[Lars]

I always try to reuse the original brass parts, jets, valves, needles etc on my bikes bikes. Sometimes the slow jets are so bad that I replace them. Done a lot of CB 550's. I haven't read anything yet about the air/fuel mixture screw, but I assume they all are correct adjusted.

It might be correct that the Keyster set is fooling around with you, but I have tried them several times without any problems. I would still not overrule a vacum leak. The symptons point to that direction... Even though your rubber tubes looks fine, they are still old and stiff. I had the same problem on a CB 750 K3 not long ago, and after replacing the rubber inlet tubes, everything was fine.

[swan]

Good ideas on the o-rings and re-check for vacuum leaks. You originally stated you did so with "multiple spray tests". I have done that as well and a friend told to me try use propane from an unlight torch instead of spraying fluid all over my clean engine looking for vacuum leaks. I used o-rings and light smear of Yamabond (fuel, oil and heat resistant sealer) between my cylinder head and carb adaptor.

To answer you questions:

-Clean OEM components per your instructions-YES
-Replace aftermarket needles with originals (I believe clips should be set @ second groove from bottom?  Will search again to confirm if you do not) YES, WITH CLIP IN STOCK POSITION (Middle slot ? for CB550) IF YOU ARE RUNNING STOCK AIRBOX FILTER AND EXHAUST.
-Pull emulsion tubes, clean tubes and passages thoroughly and carefully-YES
-Swap aftermarket air screws for OEM-YES
-Ok to leave aftermarket main jets? (OEM can be cleaned up but looks like I marred exterior of one on left a bit when removing.-YES
-Ok to leave aftermarket slow jets?-YES BUT I WOULD CLEAN AND TRY ORIGINAL PILOT JETS

[phil71]

Just use round o-rings that you can get at an auto parts store. They were known to get bad around 5k miles even back then.. which means that you'll probably do them again eventually , if you keep the bike.
 It was not their shining moment, and was corrected on the 400F and 350F.. those manifolds are part of the head.. On the 500/550, those o rings have to take an awful lot of heat on one side..
   I've wrestled with a 550 for awhile, and it PASSED the propane test... but STILL turned out to be those o-rings.

[matt mattison]

When you read your plugs, did all show a lean condition?

[Jay D.]

Thanks everybody. 

Yes, I have tried to propane test, too, and lumped that in with the WD-40 method as "spray tests." 

Would be interesting to come up with some sort of smoke test that would show where the smoke was being sucked into open spaces.  Not actual smoke, per say, but some sort of vapor like you see in wind tunnel tests.  If I recall mechanics use something similar to find A/C leaks?

Will dig into the bike again tomorrow.  I am not familiar with the airbox strap method so I'll have to do some research on that.  I have been removing battery box and airbox but sounds like I am making some extra work for myself.

I find all of this fascinating and frustrating at the same time.  However, it keeps me grounded in a world of immediate gratification.  I am learning a lot thanks to you folks and some good old fashioned trial and error.

And yes, I have full intentions to keep this bike for a LONG time.  For what I paid and the amount of sweat equity I have invested I don't see myself ever parting with it.  (Famous last words!)

[Jay D.]

When you read your plugs, did all show a lean condition?

No, they are generally reading on the rich side. 

[matt mattison]

they are just o-rings..  30.8MM (which likely means they used an SAE o-ring)  can prob source them locally. I guarantee they are hard as rocks and flattened .

Just looked a spare manifold I have - yep, they're flat and hard. Would be nice to source locally but wasn't sure if req'd specific rubber compound due to heat?
[/quo

Those o-rings are the same part number as the o-ring used on the tapper caps. Check with the local Honda dealer. They used those o-rings on many bikes for many years

[Jay D.]

Those o-rings are the same part number as the o-ring used on the tapper caps. Check with the local Honda dealer. They used those o-rings on many bikes for many years

Good call, thanks!

[matt mattison]

When you read your plugs, did all show a lean condition?

No, they are generally reading on the rich side.

If you read the plugs off idle without doing a plug chop, then being a little rich would be normal. I would tend to think the pilots are not your culprit. You must be leaning out in the 1/4 to 7/8 throttle area. That would lead me to the needle and needle jet first if all vacuum issues are known to be good. The OEM parts might help if they are all good. I just replaced 1 OEM needle and needle jet in mine recently because of wear. OEM needles and needle jets are still available for the K.

[lucky]

If the mixture is lean from pods being installed and no jet changes the idle WILL climb.