Topic: 1976 550K + 087A carbs = trouble

[gregk]

The air bleed screw modulates the air coming from the air jet feeding the emulsion tube.
Moving the screw away from it's seat allows more air to flow in that pathway.

If you don't wish to know how it works.  Then turn it out (CC) to lean, and inward (Clockwise) to enrich the pilot mixture.

Hollow tipped air screws have a limit to their effectiveness/range of adjustment.  The limits are determined by the cross drilled hole in it's tip and the pilot air jet orifice size.

Cheers,

Adjusting the air screw does not seem to make any difference to how the bike runs.   I pulled the plugs last nite and noted they were all black and sooty.  I replaced them with new D 7EA plugs (one of which would not fire) and again noted after a very short run at approximately 3000rpm that they were black and sooty again. When i was installing the plugs, I checked each one by connecting the plug wire and shorting it out against the block.  All four appear to have a nice blue spark - with the exception of one brand new plug that had nothing!  So the carbon fouling condition is  likely caused by an over rich fuel/air mixture.  If I can't adjust with the air screw, it must be in the carbs, either something plugged or float level out of wack.  If i must return to the carbs, i will under duress.

[Randy]

I'm having the same problem with my CB500k.. She won't come down or will come down slowly of acted normal..I have disconnected the return throttle cable..I think it might be lubricant I put in during assembly in the slides.. I'm looking into it this weekend..

[TwoTired]

Air bleed screws only effect the pilot circuit.  The fine tuning of these has more to do with throttle twist response than overall performance.  For a mixture control it loses most of its effect when the throttle is opened more than 1/8 of it's travel.

I'm not calling you a liar.  But, you are giving us contrary in formation.  You are saying that there is very low/no vacuum.  Yet that is precisely what draws fuel from the carb reservoirs.  The carbs feed NO fuel when the engine isn't sucking air.

How could it be running rich without it showing on the vacuum gauges?  With no vacuum, gravity on the fuel in the tank is the only force available to move fuel into the cylinders (which would indicate leaking float valves and be a problem with engine running, or not).

We are blind here.  And are working from the data you give us.  Somehow, the laws of physics are being circumvented with your description.
Perhaps the media should be alerted?   jk

Cheers,

[gregk]

We are blind here.  And are working from the data you give us.  Somehow, the laws of physics are being circumvented with your description.
Perhaps the media should be alerted?

I assure you that I am not trying to repeal the laws of gravity!
 I am going to borrow another set of gauges and recheck my carbs.  And as I have the weekend free, remove and recheck the carbs, particularly the float levels. 
Thanks for the help.

[Raef]

By opening the idol screw all the way you are allowing more air in, maybe just enough to run, albeit high, doing this would also lower the vaacum reading. Does the bike leak gas when sitting with the gas turned on and not running, that would be symptom of leaky float valves.

A good way to ensure all passages are open is to gets syringe and inject some form of cleaner through all the passages.

Mark

[gregk]

By opening the idol screw all the way you are allowing more air in, maybe just enough to run, albeit high, doing this would also lower the vaacum reading. Does the bike leak gas when sitting with the gas turned on and not running, that would be symptom of leaky float valves.

A good way to ensure all passages are open is to gets syringe and inject some form of cleaner through all the passages.

Mark

No gas leaks of any sort.  Every time i let the bike sit for a bit, i have to adjust the idle screw when I start it up.    When this happens, the idle is always way too high on startup and i have to back off the idle. 

[Nortstudio]

I'm having the exact same fouling on the plugs. All four. I know I need to go back through the 3000 mile tuneup again - but I'll be curious to see if gunked up carbs could be your issue.

 I too had no noticeable effect on the engine when trying to adjust the air screws for maximum performance (following the procedure described by TT in the FAQ I think). There was really no effect at all.

I was thinking maybe This is because of this other type of air screw TT mentioned as having less control over the mixture?

[gregk]

I'm having the exact same fouling on the plugs. All four. I know I need to go back through the 3000 mile tuneup again - but I'll be curious to see if gunked up carbs could be your issue.

 I too had no noticeable effect on the engine when trying to adjust the air screws for maximum performance (following the procedure described by TT in the FAQ I think). There was really no effect at all.

I was thinking maybe This is because of this other type of air screw TT mentioned as having less control over the mixture?

i'm going to try running the bike with no air filter to eliminate the possibility of an air restriction.  And when that doesn't work, revisit the float levels.

[gregk]

After another go at a tune up check, i decided to get a second opinion of the way the bike was set up now.  I had a friend go thru the 3000mi tune up procedure as well as remove the carbs and do a compression test.  he did confirm that regular tune specs were correct but the compression is low as well as a low vaccuum reading.  This leads us to believe that the low compression is causing the bike to run rich.  As mentioned previously, the bike has low miles ( 2500) and sat in a garage since 1977.  it is quite possible that the rings are to blame.  i've been given several solutions for the ring problem, from removing the head, to squirting ATF into the carbs while it is running.  I am going to try the easiest methods first, maybe loading the cylinders with a penetrating oil and soak for a few days. 
I did look into smaller jet sizes but there doesn't seem to be any smaller, just bigger. 

[Ryan66]

Not to thread jack but how do you know what carb model you have? I have a 76 550k

[gregk]

Not to thread jack but how do you know what carb model you have? I have a 76 550k

The carbs have a number stamped into the flange that bolts to the head.  Look on the number one or four carb and you will see it.

[TwoTired]

he did confirm that regular tune specs were correct but the compression is low as well as a low vaccuum reading.  This leads us to believe that the low compression is causing the bike to run rich. 

You are not thinking this through properly.
Do the carbs supply fuel when the engine isn't running or the crankshaft turning?
Ans: No, because there is no negative pressure (vacuum) applied to the carb throats from the engine cylinders.
The vacuum level applied, and the air speed at the venturi are what determines the fuel flow rate through the metering jets.  There is no other means to move the fuel (besides gravity).  No pumps or other positive displacement mechanisms for the fuel exist in the carbs.

Therefore, low vacuum is not responsible for rich mixtures.

As mentioned previously, the bike has low miles ( 2500) and sat in a garage since 1977.

With the crankshaft and cam stationary, some of the valves are closed and a few are open.  Cylinder walls and valve seats don't normally corrode if the valves are closed.  But it is guaranteed that some of the valves will be open to all the humidity (water) that is in the atmosphere.  This makes the iron based components in the cylinder rust, with severity related to the conditions encountered.

Piston rings will scrape away the surface rust pretty quickly.  The rust can jam in the piston ring grooves, freezing the ring to the piston and ruining ring to cylinder seal.  Rust and or the pits in the metal it creates can make an uneven surface on both cylinder walls and the valve/seat interfaces.  The conditions will be the worst immediately after returning the engine to service.
Note, it is very unlikely for rust to be the same severity for all 4 cylinders.  Some will be noticeably worse than others.
So, how bad is it?  Are the cylinder wall pits too deep to ever seal again?  Will the valve seats wear to a sealing state?  Will frozen rings in pistons ever free and make a good seal again.

Two ways to tell. 
One - Take it all apart and examine/measure the cylinder walls and all the other mechanical bits inside, replace anything out of spec. and return to service.

Two - Run it for a hundred miles with a thin oil (like 10W-40) to see if the parts will wear in again and seal.  Compression will go up on recoverable cylinders and get worse on those that aren't recoverable.  Don't be afraid of some power spurts to pound the rings loose. If all cylinders improve and are within 10% of each other, change the oil again and ride it some more.
If worse on one or more cylinders, the same parts you would have replaced on the take-it-apart method will need to be replaced now.

Which method sounds better to you?

Cheers,

[gregk]

.

Two ways to tell. 
One - Take it all apart and examine/measure the cylinder walls and all the other mechanical bits inside, replace anything out of spec. and return to service.

Two - Run it for a hundred miles with a thin oil (like 10W-40) to see if the parts will wear in again and seal.  Compression will go up on recoverable cylinders and get worse on those that aren't recoverable.  Don't be afraid of some power spurts to pound the rings loose. If all cylinders improve and are within 10% of each other, change the oil again and ride it some more.
If worse on one or more cylinders, the same parts you would have replaced on the take-it-apart method will need to be replaced now.

Which method sounds better to you?

Cheers,
[/quote]

I like door number 2!!  The compression is very low in cylinders 2 and 3 ( 100 and 105 psi) while the other two are 120. 
The low compression could be the cause of the running rich. 
I'm going to load up with a few set of new plugs and run it for a while and see what happens.  Right now the plugs carbon foul almost immediately. 

[TwoTired]

The low compression could be the cause of the running rich. 

I don't think so...  What do you base that theory upon?

I'm going to load up with a few set of new plugs and run it for a while and see what happens.  Right now the plugs carbon foul almost immediately.

All four?  Even the ones with good compression?
If they are all fouling the same despite compression, you still have carb issues.

Cheers,

[englishwheeler]

I've got these EXACT same issues with my 1976 cb550. What I've done is a compression check....125-130 across the board. I have taken the carbs off and cleaned every bit of them. I have also adjusted and double checked the float levels...all currently at 22mm. Timing was checked and the carbs were synched.

It is very hard to get my bike started. My choke only makes things worse. Once I get the bike started it will idle very rough. I can hear short runs of improved idle...it's almost as if the other cylinders aren't firing correctly at times...then they are at other times. Turn the choke on and the bike dies quickly.

I must mention I have the ever controversial pods on mine...so I expected problems. However, I didn't expect the same problems as someone with a stock intake. I have a 4-2 exhaust.

I, too, notice no effect with the idle mixture screws. I can ride the bike, but keeping it running at a stop sign is tough. Taking off is really tough too...I have to slip the clutch and give it some high revs. Once I get above 2000-2500 rpm I'm good. I can even run the bike down the street in 3rd or 4th gear at around 2000rpm with no real issues.

I've tried Autolite plugs with tapered electrodes as well as the D7EA plugs. Neither seem to make a difference. It's very frustrating. I can't tell if it's running rich or lean with the way it's acting...so I don't know what to do about the pilot circuit.

I was hoping that PD46C carbs would fit this bike so I could just mess with jets. Not sure what I will do if I can't figure it out.

[TwoTired]

Check battery voltage.
Check voltage and connection integrity at the coil connectors (B/W).

Always a good to perform the 3000 miles tune up checklist.

You check timing.  Did you check the point gap (effects coil charge time).
How old are the condensers?  Have they been allowed to lie fallow without voltage applied to them for a very long duration of time?
Did you measure the plug cap resistance?
Do the coil wires have cracks in them?  In a darkened garage, can you see sparks from the wires jumping to engine or frame?
Do the deposits on the spark plugs tell you something?  And, are they all show the same deposits.

Is the the gas tank free of rust?
Is you in tank filter damaged? (Or present?)

Do the carbs fill to the same level, 1-2mm below the bowl gasket.
Do you know any of the carb internal settings?
Do you know if they were tampered with?
Do you know the emulsion tubes are clean?
The pilot screws change idle mixture and response to throttle twist on this model.  What setting have you chosen?
Are the carb internal parts from Honda, or aftermarket?
Did you vacuum sync the carbs or just bench sync them?

"Pods" is not a specification, it's a style.  State brand and type; oiled foam, paper, gauze, filled with peas, etc.  When were they last cleaned?  Does the engine run different without them installed?

If you get the pd carbs, you should get them together with the manifolds and rubber couplers.  You'll need a choke cable, too, as well as throttle cables.

Good luck!

[Duanob]

OK since I'm not the only one who has overlooked this manual, I would suggest downloading it and read it! It explains a whole lot on how these carbs work including diagrams and pictures. TT can explain until his fingers are blue but until you see cut-aways on the different airways and jets and how and when they actually work, you just won't get it. Then TT's advice will make perfect sense.

http://www.mediafire.com/file/c1wk828k2wtri5i/Motorcycle%20Carburetor%20Service%20Manual.pdf

I went through my carbs I thought pretty good until I read this. Then I took the needles out cleaned them up real good, dropped them down two slots. Then vac synced the bike. It ran way better with more low to mid range response but the plugs were white and starting and warm up took a long time. Then I lifted the needles up one position and now the bike starts and runs better than ever. I went from sooty rich deposits on my plugs to white and then to a nice tan. All my jets are OEM honda as well as the airbox set up and 4x4 exhaust. Sometimes it just takes trial and error to learn what the bike needs. Understanding how it works is the first step.

[Nortstudio]

Can we get a TT confirmation on what size slow jet is stock on the 087a carbs please. 

I could have sworn that it was 38, but Duanob thought 40.  When I went back to check the carb set-up sheet for 500/550s, broken down by year, it lists "1974-1976 CB550k" as having 022a carbs, with 40 size jets stock.  I have 2 sets of 087a  carbs for my '76 550k, and they both have 38 jets in them. 

Thanks

[Ryan66]

My 76 550k 087a carbs have a 38 slow jet stock

[TwoTired]

#38 is standard for the CB550.  I did find #40 in my 74 CB550K, and I know those were stock from history with it since way back in 1975.
It's the only one I found #40 022A carbs.

Below is from a Honda mechanic's shop booklet.

Cheers,

[Nortstudio]

Thanks TT.  I was going off of this chart.  Not sure where I got this, but I'm sure it was on here somewhere.  It doesn't mention 087a at all.  PS.  Sorry I never got to do the measurements for the 022a.  The rack I got was corroded together as one solid piece.  Could not get the jets out, couldn't get the float pins out, nothing!

At least I know I'm not crazy...about this at least. 

[TwoTired]

I made that chart many years ago and donated it.  It was placed in the FAQ.   I made some assumptions.  Like... my 74 CB550 was "representative" of stock, since that's definitely the way it was delivered by Honda.
I have a new chart with a lot more data in it, including 087a measurements.  However, I now have doubts that my 087a set was actually in untampered stock condition.

Live and learn...

Cheers,

[Raef]

Another thing to keep in mind is year to year roll over, I have a 550 f, I bought from the original owner with 8500 miles on it.
According to the serial #"s and man date it is a 75 but it is titled as a 76 F and it has 40 slow jets and the carbs are numbered 022A.

I have know idea the how or why, just what it is. The bike sat for about 20 years and It took a good while to sort it out, most of the problems went away when I restored the filter system inside the tank and rebuilt the petcock.

[Deltarider]

According Honda's Parts List they should have #38 slow jets.
http://www.hondacbfour.com/download/pdf_spac/pdf_spac550/CB550K_K1/CB550K_K1_04.pdf
If the bike was mine however and had the #40 jets I personally wouldn't bother to change them.
I'd appreciate a correct setting table for the 500/550 series. Even that mechanic booklet (Honda America co) is corrupt, I'm afraid (500).
There are still some riddles. What happened to the 069A carbs between the 550F1 and F2. When the F2 was launched, it performed worse than the old F1 and (even worse than the old 500). Yet these carbs have the same stamped number (069A).
Was the exhaust modified? The intake?

[Deltarider]

The intake?

Studying the parts list for the CB550F/CB550F1 and the parts list for the CB550F2 I notice the airfilter case and the plenum have been modified. The airfilter cases in the pictures look different. Maybe someone who ones both a F(1) and a F2 can compare.