Black smoke and hanging idle after a full rebuild

[K2-K6]

Certainly the original airbox is preferred and particularly good on these Honda, but I believe the general view out on the big wide interwebs starts with false assumption (well aren't many assumptions false?  ) in how they approach running alternative intake.

That assumption seems to be grounded in "well it's now getting more air so it'll need more fuel" and partly promoted by filter manufacturers claim in the improvement their offerings deliver.

For a std engine that's not true, but more that the change alters the carefully designed vacuum gradient that honda made and jetted the carbs for.
Essentially,  and for the same engine speed, the carburettor now enacts less vacuum and so draws less fuel from float chamber at the same engine demand. It's that which makes it run lean.
Inevitably you'll have to respond with some tailoring of fuelling to bring it back to a normal level, you'll have to add more fuel to less vacuum to bring that change.  Making a jet larger just allows that vacuum to pull more fuel through that jet as it meets less resistance.

Knowing what to add at which point is the part that's difficult to determine.

For a start point it's worth leaving the main jet alone and standard, but lifting the needle one notch.
Going up one size on idle jet,  but starting with airscrew out 1/4 turn from specification. 
Worthwhile using at least NGK 8 grade plug to help avoid overheating the plug tip.
Note;- increasing BOTH idle jet size and main jet will usually make it too rich at large throttle opening as the two changes are accumulated, the idle jet adds volume right across all carb opening.

To the OP,  which size idle jet have you used?

[thomaspigeon]

Thanks for taking the time to explain this @K2-K6

I think restarting to square  one is probably a good thing. Now I’d really like to buy an OEM needle as the aftermarket ones at troublesome apparently.

My current jetting is :
Main 110
Idle 42
Clip on the 3rd position from top

I still have the original ones so I can do this.

I’ve got D7 grades plugs so that should be ok on that side.

One last question, I didn’t apply any oil on the K&N pods. I believe applying so K&N pod oil might increase the resistance so I’ll probably do this too.

[fogrider]

After all the tests and trials I've done to get my 550 fuelling right, with foam filter , paper filter and no filter at all, it looks to me like all you're settings are way too rich.
 I think you have the 069a's like mine, if so, start again with 38 idle, needle in 2nd from top clip and 98 or 100 mains with air screw 1.1/2 out, and take it from there.

The idle jet seems  especially important, I've just discovered my idle settings were  badly effecting the whole system, after the knack***d float needles and valves were changed, float heights set, richness from the idle system had me chasing ghosts. Idle jet checks out as  41 ( marked 38 though) and seems to be way too big. I'm going to try some 35's just to prove a point.

All part of the fun.

[K2-K6]

"After all the tests and trials I've done to get my 550 fuelling right, with foam filter , paper filter and no filter at all, it looks to me like all you're settings are way too rich."

As you find, there's delicate balance and shift around the lower end carburation, and more complex with the K&N type pods.

They effectively add another layer of pain with both the bell mouths and still air box removed.

I'd still start with just the idle sized up along with the setting changes as a first look as it'll give us a picture of response and something to go on.

[robvangulik]

Does the black smoke persist with the k&n's removed?

[thomaspigeon]

@robvangulik I didn’t try this yet.

@k2-k6 and @fogrider I started to reset the carbs after work as all this news got me really excited to try. I didn’t have the time to finish but hopefully I won’t get out of work tomorrow.

I’ll probably try a idle jet at 40 just to see

Keep you updated

[thomaspigeon]

Hey guys,

So good news, no more smoke and no more hanging idle! Now the midrange were weak so I lifted the needle to 3rd position from top. This fixed the problem quite well.

Low revs are struggling to pick up so I believe I’ll need to play with the mixing screw (current idle jet at 40 and I’m still 1.5 turn out). But will do this tomorrow evening if I have the time.

Also from 3/4 to full throttle its really not picking up. I suppose I’ll need to change the main jet to 100 to try maybe 105 but I don’t want to cut corners.

It’s the first time I started to get some sensations on the bike and felt like it’s actually running! I could almost take it out like this. But I’ll take the time to have it running a bit better before I go for an actual ride.

Thanks a lot for your help @k2-k6 and @fogrider! Keep you updated

[K2-K6]

Good progress,  and now a clear picture of individual elements to work on.

Yes to change the initial pickup in adjustment of airscrew inwards to then try like that. If you found that you end up below about 3/4 turn out from closed it would indicate that a small step up in size of idle jet would be ok. See where you get to first with this one though, and it will usually look different to with a std airbox so a little unconventional setup is to be expected in making it work.

Something that seems to help is to use R Plugs as well as R caps and set plug gaps to their absolute minimum in manual specification.  It's beneficial in weaker mixture running and helps prevent the engine dropping into a flat spot at mixture margin. If you want to try that, then use NGK R 8 rated plug. It also (#8) reduces the risk of the plug tip getting too hot and being compromised.

[deltarider]

... and set plug gaps to their absolute minimum in manual specification... 

This ^!!
Recently I have bought a set of 4 DR7EA plugs (I run silicone non resistor caps). When checked, I was glad to see, they were already set to the minimum by NGK: 0,6mm. Whereas the D7EA plugs, that I've bought years ago and that are still new in their boxes (for if I ever return to resistor caps), are gapped a little wider. Coincidence?

[thomaspigeon]

hey,

So I went from #38 idle jet to #42 as the idle was hanging a bit and I couldn't close more the mixing screw.

I didn't have the time to play too much with it but for now it looks promising. At 1.5 turn out it's running a bit lean/ hanging idle and at 1 turn I have some black smoke but no hanging. So the right balance is in between this 2.

It feels like full throttle is not very powerful, I'm still at #100 on the main jet. But I think 105 is a bit too much as I already have some black smoke. I never had a running CB550 in the past so I don't know how powerful those engines should be.

I might have some DR8EA plugs kicking around but no R plug caps. @deltarider are you saying that I can run regular caps with R plugs?

Also last thing, engine seems a bit noisy and also jumpy when decelerating - accelerating. Like the cam chain is a bit loose. My tensioner screw doesn't seem to function properly (it doesn't do the spring return effect). Some people are doing the cam chain tensioning while the engine is running, is that a good idea?

Thanks for your help, it's getting there!

[deltarider]

... I might have some DR8EA plugs kicking around but no R plug caps. @deltarider are you saying that I can run regular caps with R plugs? ...

Sure you can. So far I have seen no proof of a positive effect by adding more resistance than the 5kΩ that either a R plug or a resistor cap provides. The discussion pops up every now and then in the international forum, but I have yet to see a falsifiable result, meaning it can be reproduced. In my opinion the plug gap - more or less wide - is far more determining spark duration. 

... Some people are doing the cam chain tensioning while the engine is running, is that a good idea?...

I have to do it like that, as my tensioner bolt is not properly functioning, but I can not recommend it, unless you have to. Do not expect to SEE the bolt turning when the lock nut is loosened. It moves just a fraction! Also do not expect too much result of adjusting the tensioner. Often the culprit is in the ignition or carbs that are not balanced well.
CB500/550 owners are advised to have a look at this video shot by René van Maanen of Honda4.nl. It gives you an idea how the tensioner works and why you will not even see the bolt turn when you loosen the locknut to let it adjust. It will move just a fraction. Also do not expect a wonderful humming engine after adjustment. You will always hear the camchain.
Mind you, the vid does NOT show how to perform the adjustment, it only demonstrates what goes on.To adjust, either do it by the book or like Bryan suggests.
I do NOT recommend to do it with a running engine like Honda's Owner's Manual CB500K3-CB550K3 suggests. I don't know why it is there. Could have been an error in editing by copy and paste.
https://www.youtube.com/watch?v=8qJc6e5pa8M
Courtesy Renë van Maanen - Honda4.nl

[thomaspigeon]

Hello everyone,

After countless carbs disassembly and reassembly. I start to see the light at the end of the tunnel.

I'll try to get through the process briefly :

1) I first went for pilot #42, main #98, 3rd clip position
2) Soot and smoke was building up, idle was hanging when up in the revs
3) Changed the spark plugs for DR8EA but it wasn't firing properly and flooding so back to the D7EA
3) Went for new O-ring (thanks Nurse Julie and Fogrider) for the mains and put back OEM needles and emulsion tubes
4) Very little difference but slight improvement in the riding qualty though still soot and black smoke and hanging idle
5) I measured how much petrol were in the bowl, between 50ml and 60ml (is that too much?)
6) I went for pilot #38, main #110 (I don't have any #105), 3rd clip position
7) Somehow some carbs started to leak petrol from the overflow massively and flood the pods (and so the engine)... taken them out to fix this...
7) NO MORE SMOKE! NO MORE HANGING IDLE! 

It really starts to run well BUT it's struggle to take off when hot and sometimes stalls, I really have to rev it to take off. Once rolling it's fine. Basically low revs are bogging. It's idling fine though. If I wait at a red light and try to go it's really boggy like it's building up. I tried to play with the mixing screw but very little difference on this problem. I struggle to put it in Neutral so I guess carburetion is not quite there, yet!

Now here are my different thoughts :
1) Some carbs are still leaking very slightly from the overflow (like a drop or so but only when riding) and I kind of find a bit of petrol under some pods, if the level is too high in the bowl, could it flood the carbs? I don't have any smoke though but I tested late this evening maybe I didn't see it.
2) Clip position is too high so it's running too rich when accelerating
3) I need to go for #40 pilot jet
4) Get the DR8EA back on to see if it helps to fix this

Let me know what your thoughts are on this one,
Thanks

Tom

[fogrider]

Tom, I had confusing symptoms on mine, it always seemed really weak just off idle, gasping/bogging, but never any black smoke.  I finally found the idle circuit was over-feeding the full range, even though it ticked over OK. Idle jets measured as 41.
Long story short, it needed SMALLER idle jets, contrary to the symptoms. 35's have cured it , completely. Got 'em in a cheap aftermarket kit for a CB350.
It seems  illogical, but it worked (for me anyway).

I think it was the American side of these forums where I read two owners with EXACTLY the same issues. After trying everything, it looked like they finally gave up and flogged their bikes, I reckon the illogical step of smaller idles would have made them happy owners too.

Good to see you don't give up easily.

[Trigger]

I have found over the years it is very hard to advise on carbs as, they all have different worn out parts. And all have different engine's in different states. You can be chasing a carb problem for years if one head valve is leaking 

[fogrider]

Quite right, the older the bike, the greater the mileage done, messed with by previous owners etc, plus going by previous experience can be misleading too. Until I put the Lambda sensor in I was convinced there was weakness causing the problem , the symptoms seemed pretty clear, I wasted a lot of time trying to resolve weakness.

The Lambda showed the reality, or I would be still chasing it now !

She was badly neglected so lots of things to resolve all at once which did'nt help.

Keep at it Tom, it's all part of the fun......