Topic: CB550 Carburetor Replacement ideas

[Amann31]

Hey guys, so I have had my 1976 CB550 for a few months now and have been riding often, but I could never get it to idle quite where it should. It always wanted to idle at 1500-2000 rpm (according to my tach). Anyways, it recently began to die at idle once  fully hot, which made me finally bite the bullet and open up the carbs. The #2 carb looked like this:
For context the #2 cylinder had acted strangely and I suspected it of having some kind of misfire, despite strong ignition. Anyways, to get to the point of my long winded story, does anyone have any ideas on fixing or replacing just the #2 carb? I would hate to buy a whole other rack on ebay and have to worry about it being in usable condition or not. Thanks guys.


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[Amann31]

Also found a Murrays 4into2 carb setup on ebay for 450 and I am considering that if these seem unfixable. If anyone has an opinion on these that would be awesome. It seems that the #2 carb certainly is unfixable due to the broken piece being part of the casting.


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[Deltarider]

Looking at the picture, my main concern would be where the main jet sits. You have to make sure the main jet is well sealed, meaning: no gasoline can be sucked passed the little O-ring. That tower looks a bit damaged. I hope you can improvise semething. Others may chime in with advice.
For the rest, I don't see anything wrong. I'd carefully unscrew the SLOW JET and clean it. Prior to that you may want to spray some WD-40 or similar product first. For cleaning some carb cleaner and blown air usually does it. I sometimes use stranded copper wire for it. Trying to look through it, you may 'detect' something in there that looks like some sort of a minuscule spider web. Ignore it: it's not there! It's a known trompe l'oeuil, an optical illusion. You may also blow some air and carb cleaner in the orifice of where the SLOW JET sits. I'd carefully pull (try with your nails) the float's swivel pin and clean/polish it. The same for the conus of the float needle and its corresponding seat in the valve. You may leave some WD-40 on the contacting surfaces, so the needle won't stick. Once reassembled, the gasoline will take it from there. You don't want to use anything abbrasive. Do NOT be tempted to 'adjust' the float's tang. I have never seen a CB500/550 float tang that needed to be readjusted. Many here - eager to do 'maintenance' -  interpret the Clymer manual on this as a maintenance thing. Well, it's not.
BTW, you haven't specified your model CB550. Just mentioning the year doesn't give us a clue.

[Oddjob]

What number is on the carb body, number 4 is easiest to spot as it's usually stamped on the outside of the mounting flange ear at the front of the carb, could be 627B or 069A for instance.

By the look of it someone has been mucking about inside the carbs, I hope they aren't all like that. I can just make out 110 on the main jet and that's a big increase on standard which is normally 98 on a 550.

Pieces missing out of the main jet tower AND the float tower, I'd check the pilot jet size as well to see if that's still standard. I'd also check the float height. It still running the standard airbox or has someone fitted pods for instance.

1500-2000 is far too high for a tickover, 1000 is standard and if the engine can do that without making any undue noise it's the sign of a decent engine in fine tune, however most aren't these days so tend to have the tickover increased to compensate for internal wear, 1200 is usually the norm for doing that. Any higher and you really have got some internal wear going on.

Check all the other carbs for damage, might be easier and cheaper to just replace number 2 carb. They are handed so only a number 2 carb will do BTW.

I do have some carb spares, including bodies so I may be able to help.

[Amann31]

Delta, thanks for the advice and that tower damage is exactly what has me concerned. I knew that the #2 cylinder was not running well for a week now but didn’t know the cause until I opened up the carbs. My theory is that there is essentially a huge vacuum leak in carb #2 thats forcing the idle of the whole engine up and making #2 run lean. Also the bike is a k1 I believe.
Oddjob, I am not sure that anything I can improvise to fix the tower will hold up and be in spec. I thought for a second about some kind of epoxy or JB weld to rebuild the tower, but I would definitely rather simply replace the carb body. Looking online I can only find full carb racks or carb #3. As for what carbs they are it is 069A. If you do have just a #2 carb I would be happy to buy it, unless you guys think these Murray Carbs are worth it. I got him down to 375 for the set and I am waiting to pull the trigger if someone has any opinions on them. Thanks


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[Amann31]

Also the main jet is a 115 and the pilot is a 40. The bike has pod filters and a open 4into1 exhaust, not sure about the brand. I am at sea level  and I figure the bigger jets should keep it from running too lean with the increased airflow from the pods.


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[Stev-o]

069A carbs came on the 550F Supersport model, is that what you have?  Personally, I would not buy Murrays carbs, I have not read good reviews on this forum about them.

Most likely, the jet holder was corroded and they "repaired" it with JB Weld [or similar]. Have you checked the other carbs for similar repairs?

If there are, I would sourced a good set of the proper carbs for your bike and the correct airbox would be a good idea too if you want it to run properly with easy tuning.  As far as buying used carbs, I would just assume they need to be gone through, clean carbs are one the most important things to have a good running bike.  Good luck

[Oddjob]

I do have a Number 2 carb, in fact it's this one.



I was mucking about 1 day and decided to see how well I could polish a carb body, 1.5 hrs later that was the result. However it's only one side, the other side is still that dull grey.

I'm willing to sell but bear in mind I'm in the UK and postage may not be cheap, or it may be, I would much prefer you however to check the rest of your bank first and see if any others of the bank are showing the same type of damage, I think I've sold number 4 and number 1 carb was always wrong as it was a 627B body on a rack of 069a carbs, hence why I decided to split them. I may still have number 3 or it may be number 4 if my memory is faulty.

Check first and see. It's not quite as bright as it looks in the pic, time has dulled it a little, the body itself is in great nick, no corrosion anywhere I can see. Choke flaps are removed as it everything else, you can swap all that over from your old carb if you end up buying it.

Let's see first how the rest of the rack looks.

[Amann31]

Stev-o, I believe that according to my VIN I have a K1, so a PO must have swapped the carb rack to the 550F version. Each carb is a 069a model. I just took a quick look at the other two carbs and they have some corrosion, but all look serviceable.
#1 carb ^

#4 carb ^


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[Amann31]

Oddjob, I would be interested in buying your #2 carb as even with shipping across the pond I am sure it would be cheaper than a whole new rack of carbs or these Murrays.


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[Oddjob]

Those pics look to be of the same carb, number 4, there should be a choke lever visible if it was number 1.

The appear to show damage consistent with water being left in the bowls, that corrodes the towers over time and leaves that dimpled effect.

Oring in the first pic is buggered, clearly moved when the bowl was being fitted and crushed it. How's number 3 carb?

[Amann31]

Those are 1 and 4 and the number 3 carb is similar with the same dimpling on the main jet tower. And yes the o rings are pretty terrible but I plan on rebuilding all of them before reassembly.


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[HondaMan]

Also found a Murrays 4into2 carb setup on ebay for 450 and I am considering that if these seem unfixable. If anyone has an opinion on these that would be awesome. It seems that the #2 carb certainly is unfixable due to the broken piece being part of the casting.


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I'll +2 that Murray's carb don't-use post above. I've got a LOT of email (not from this forum) about major troubles with the Murray setup. Idle with them is in the 2500 RPM range at best, and the flat spot before 4000 RPM has to be experienced to be believed. It's just too much volume for the intake valve size in use (too much for the piston size, too!).

That damage was done by MTBE fuels during the 1980s. It checked and weakened the post and the PO probably installed a thicker O-ring to try to seal around the jet, only to have it break off the side of the post. I have some 1.1x4mm O-rings to help with the now-oversized holes in all 4 of the carbs (but it won't fix up the broken one) if you need them. The O-rings in any gasket set you get for these now-eroded carbs will not seal very well, letting fuel slip past them and making for rich running problems that cannot be controlled (it is unmetered fuel). Honda's own gasket sets have a correct size if they are not too eroded: mine will help if those will not hold the jets snugly in place. I have NEVER seen any aftermarket gasket set for these carbs that have the correct O-ring for these mainjets, not since about 1995.
PM me if needed.

[Oddjob]

That damage was done by MTBE fuels during the 1980s.

I have NEVER seen any aftermarket gasket set for these carbs that have the correct O-ring for these mainjets, not since about 1995.
PM me if needed.

Never heard of MTBE fuel Mark, is it an American thing?, we only tend to see damage like that when the bowls are water contaminated, otherwise ours seem to last just fine. Due to our climate in the UK we also don't get winter and summer fuel, same fuel all year long.

As for the oring sizes, pet hate of mine this, sellers will supply whatever they think will seal, doesn't matter how long it seals for, just so long as enough time lapses that you can't return them. They won't go to the trouble of having them specially made as the minimum order is 500, that makes them expensive to buy due to the amount of sizes in a carb rack, I priced up the 500/550 rack and got an initial outlay of close to £1000 to have them all made to the exact size Honda specified. Same applies to the inlet and tappet covers rings, tappet covers aren't a huge problem if they leak but the inlet manifolds are, and they are a #$%* to replace as you need to remove the carbs and we all know how bad a job that can turn out to be. I've seen sellers supply rings so bad I refused to fit them in the inlet manifolds and fitted an old tappet cover ring instead. I have quite a few genuine Honda head sets and as you know they supply 12 of those rings in each set, from now on I'm saving those rings specifically for inlet manifolds, I can fit close enough rings in the tappet covers until I have those made to order as well.

[carnivorous chicken]

There are rebuildable sets of 550 carbs on Ebay for $160 or so, and of course more expensive as well. Rebuilding stock carbs yourself is the one way to verify it's going to run like it was meant to.

[Oddjob]

Unless the seller posts a pic of the inside of the float bowl area I tend to avoid buying them unless they are dirt cheap, far too many with broken towers these days. Although someone came up with a solution to a broken float pin tower which works really well. A corroded main jet tower though is a big problem.

[carnivorous chicken]

If there aren't photos of the insides you can always ask...

[Amann31]

Figured since I am going to replace the #2 carb anyways, i tried to repair the post with some jb weld. Looks like jb weld is gas safe, so I built the tower back up.
Ended up looking like this^
I tested a main jet in there and the o ring seems to seal well but i am wondering what a good way to test the seal would be without putting everything back together and tying to run the engine.


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[Oddjob]

Fit the jet with the oring on, block the jet hole with a suitable tape. Turn upside and fill the tube up with petrol, must be petrol as nothing else tends to try and escape like petrol seems to. If it doesn't leak your good to go I reckon.

[HondaMan]

That damage was done by MTBE fuels during the 1980s.

I have NEVER seen any aftermarket gasket set for these carbs that have the correct O-ring for these mainjets, not since about 1995.
PM me if needed.

Never heard of MTBE fuel Mark, is it an American thing?, we only tend to see damage like that when the bowls are water contaminated, otherwise ours seem to last just fine. Due to our climate in the UK we also don't get winter and summer fuel, same fuel all year long.

As for the oring sizes, pet hate of mine this, sellers will supply whatever they think will seal, doesn't matter how long it seals for, just so long as enough time lapses that you can't return them. They won't go to the trouble of having them specially made as the minimum order is 500, that makes them expensive to buy due to the amount of sizes in a carb rack, I priced up the 500/550 rack and got an initial outlay of close to £1000 to have them all made to the exact size Honda specified. Same applies to the inlet and tappet covers rings, tappet covers aren't a huge problem if they leak but the inlet manifolds are, and they are a #$%* to replace as you need to remove the carbs and we all know how bad a job that can turn out to be. I've seen sellers supply rings so bad I refused to fit them in the inlet manifolds and fitted an old tappet cover ring instead. I have quite a few genuine Honda head sets and as you know they supply 12 of those rings in each set, from now on I'm saving those rings specifically for inlet manifolds, I can fit close enough rings in the tappet covers until I have those made to order as well.

I guess (and rejoice!) that UK never suffered the MTBE additives. They were designed to ruin older engines, particularly those with simple cast-iron or aluminum-zinc alloys in the combustion process. The US DOT ordered it in 1984 (thanks, George Orwell?) and it went into effect in the early 1990s here, everywhere. It was aimed specifically at carb'd engines, to damage the carbs slowly beyond use and force the owners to stop driving the cars (and 'upgrade' to fuel injected cars instead). It was totally by accident that we discovered that Marvel Mystery Oil (among others) would hold the MTBE in suspension and prevent it burning into an acid in the combustion process, which is how I saved my 750 and several cars that I had with carbs. It still did eat away the front weld joints on the muffler in the cars, though, making them "rust out" from the front instead of the back - which was where they used to rust out in the 1960s. I put stainless-steel (18-8 grade) piping and mufflers on those cars after that, stopping the MTBE cold. If we could have had that in our bike exhausts, it would have been great! There actually were some SS exhaust systems made for the 750 that I know about, but they were/are 4-2 systems, not 4-pipers. I installed one in the 1990s sometime for a guy locally. They did NOT bend a bit if needed, but the head port positions were at least accurate and fit OK.

[Deltarider]

We had and still have some MBTE in gas. Holland was the biggest producer and maybe still is, of it in Europe. I have googled. So far I have only found bad effects on the environment, in particular groundwater which becomes smelly of gasoline. California and Maine were the first states that phased it out for this reason. After lead was gone, MTBE was meant to improve combustion. AFIK in Europe up to 15% is allowed. I don't know how much is in it now. In Sweden it's 2%. US used to have 30-40%!
I will look further for any reports on bad effects for our engines, but so far I haven't found any. Not that this means something. I'll try to find out more. Maybe the high percentage the US had, was to blame.

[Amann31]

I did test out the repaired carb body for leaks and it seems to be holding. I am waiting on a rebuild kit and I will try it out once that arrives.


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[Oddjob]

You want me to wait to see if you need this spare carb. Doesn't bother me either way, someone will need it someday.

[Amann31]

Yea that would be great if you want to hold off on your carb for a bit. I will see how this repair setup works. Thanks


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[Oddjob]

Sorry to resurrect this but I've just been reading on the UK forum abut air passages etc. There doesn't appear to be a circuit diagram for these carbs so you know where they run and where they come out etc, so you'd know the idle circuit was blocked for instance if you fed air in one place and it didn't come out where you expected it should. Maybe there is one around? if there is please post a link, I'd find it interesting.

So that got me thinking, Amman has bought my No2 carb so his old carb is essentially junk, how about sawing it in half and posting a pic? we could see what's going on inside and it may benefit everyone who's trying to work out why the engine struggles to tick over for instance. Just a thought. Or maybe someone has already done this?

[Deltarider]

Maybe this helps. From 08:30 on in:

[Oddjob]

Not really, I don't speak german that well and a real view of the galleries would maybe help to understand why they block, maybe they narrow at one point for instance. I have quite a few carb bodies BUT none that are scrap or I'd cut one in half myself, the only one I know for sure is Ammans, so I thought I'd see if he was willing to help out.

I've blasted all the galleries in mine and I know where they come out, what I'd like to know for sure is that they are where I think they are, the idle circuit for example comes out in 3 places IIRC, all must be blockage free in order for it to work perfectly.

[Deltarider]

The idle circuit has 4 openings. The one in the carb mouth will never be blocked as long as you use genuine Honda cellulose airfilter elements. Me thinks Marco explains it really well when he indicates the routes with his red straw. BTW, you can opt for English subtitles, alas...  translation is not perfect. The galleries are wider than the jets, so I don't see much of a problem there.
But for me it is easy to speak; my carbs have never been inactive for any longer than say 5 months. Moreover in winter every two months I drain the carbs and then crank the engine so the downgoing pistons can suck the jets dry. Then I let the floatbowls fill themselves again. This takes longer than you may think.  In principle gasoline cleans really well. When carbs have been left for years, it's another story and you may have to opt for ultrasonic, but... it's not a guarantee, three companies specialised in this service, informed me. There is a good video about how to do it the right way, but it's also in German:

Note that there are quite a few things one can do wrong*. Cleaning the outside of the carbs is a relative fruitless indeavour imo. After a ride they will be dusty as before. No problem when the seals are OK. The carbs on mine show a nice contrast: outside dirty, the interior... spotless, sterile.
* And in these two video's Vergaseronkel demonstrates how you can perfectly clean our type carbs (CB350F/CB500 Four) without separating and ultrasonic treatment:

and

[Amann31]

Yeah I would be willing to chop the other carb in half for science and Il post some pictures. Do you think cutting along the fore and aft centerline along the middle of the intake hole would be best?


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[Oddjob]

Probably, as the idle jet outlet is right in the centre of the inlet tract, so it should show where other drillings are intercepting it. That’s the theory anyway.

[Deltarider]

The best demonstration (so far) I have seen is Marco's.
From 14:45 - 16:00 it is about the main, from 16:00 on it is about the 'slow' route.

Good luck in cutting the carbs so precisely that we will be able to see more of the inside. Personally I hold it for impossible. On the other hand... someone has managed to cut a #40 slow jet in exact halves (see pic). Maybe scanning could bring results. In ports they can scan even sea containers for drugs, weapons and what not, so who knows. Question is... who has access to such a scanner?
I do not agree on everything Marco has chosen to do.
a) I never felt the urge to separate the carbs from each other.
b) I would not tap the needle jet into position. I just manually press it in as the main jet will fix it in its position, due to the leaf spring which in its turn will force the main jet upwards.
c) I would not have chosen Keyster parts.
d) Marco sets the airscrews at 1,5 turns out, which - in my experience - is too lean for a CB500 to provide good driveability in acceleration. For our CB500 models one turn ⁺/_- ¹/₈ was advised by Honda. It wouldn't surprise me if Marco, on finetuning, had to turn them in a bit. BTW, I hold the carb setting data concerning the CB500-A in that booklet, edited by American Honda in 1977 for an error (see the concerning note in the overview below).   

[HondaMan]

This sort of a chip off the mainjet holder is tough to repair for the long haul. I have a local welder who can do it, but the cost is like another set of carbs, plus rebuild kits(!). I've only done it once with him, but he is the most amazing welder I've ever met: he went with me through a 4-step reweld-mill-reweld-mill (repeat 4x) on a sandcast 750 engine case set some years ago, and while painful, we managed to save the engine. He always yells at me when i bring him this stuff, but I think he enjoys doing artwork in weld.