Topic: 1974 CB550 - Carb Pitting/Corrosion

[TPIGroove]

Hello all. I recently started to dig into my carbs to rebuild them, and immediately upon taking off the bowls was greeted to a rather ugly sight. Two of the bowls were bone-dry and had no issue, but the other two were wet and have a fair amount of damage. How much damage is too much? Can these two units be salvaged, or would I be better off finding another set of carbs?

[robvangulik]

As long as the main jets sit and seal securely I'd say go ahead and use them, I've seen worse.

[TPIGroove]

As long as the main jets sit and seal securely I'd say go ahead and use them, I've seen worse.

I can see the O-Ring on this one fairly easily. The other one isn't as bad. Seems like it's about halfway down the ring. Pressing on the jet hides it.

[robvangulik]

With the float bowl mounted there will be pressure on it, so it should (could) work. You'll find out soon enough anyway, that pot will run rich if that o-rings leaks. But in my eyes it'll be ok.

[Kevnz]

Build it up with JB Weld?

[TPIGroove]

Build it up with JB Weld?

I thought about that, but would JB Weld survive sitting in modern gasoline?

[ghostdevil273]

From my experience "JB Weld" will hold to gas I fixed a dirt bike carb with it years ago still using today on my friends from 
quote from JB Weld website
"When fully cured, J-B Weld is completely resistant to water, gasoline, and about every other petroleum product or automotive chemical. For wet-surface or submerged water or gasoline repairs, try our SteelStik or WaterWeld."

[TwoTired]

There used to be a member here that could weld material back on carb bodies.  Jim did micro welding and repaired several members carbs, as I recall.

I thought it was Jim's microwelding.  But, my search FU isn't good enough to find him in the members list.

Cheers,

[TwoTired]

Jim French

http://www.jmfmicroweld.com
Call him about fixing your carb bodies.

Cheers,

[TPIGroove]

Jim French

http://www.jmfmicroweld.com
Call him about fixing your carb bodies.

Cheers,

I'll probably get in contact with him and get a quote. I found the correct body on ebay for a bit over $50, and I'm stopping by a salvage yard tomorrow to see if they might have anything. You have any idea how much he charges on average?

[scottly]

IIRC, Jim can't repair the corroded main jet towers? He can weld broken float posts.

[dave500]

try and find a whole set?

[pjlogue]

probably cheaper to find a good used set of carbs on ebay.  I am curious as to what may have caused that eating away of the aluminum.  Possibly Ethanol in gas?  I know that when moisture in Ethanol gas reaches saturation the Ethanol/water separates and the resultant Ethanol/water mix is quite acidic and sits at the bottom of the carb bowl.  What ever was in the bowl on the two carbs was pretty deep because the etching is a good ways up the posts.  If a bike were parked a long time (a few years) with the petcock not turned off it would allow replenishing of evaporated fuel in the bowl and could cause what you see. 

-P.

[Little_Phil]

That's the worst I've seen. I would replace. Seems to affect lots of US bikes that have been left. Not seen it on UK bikes. Maybe ethanol, the US has a long history of using an ethanol mix, back to the 70/80s. I have a US bike that was stored for 40 years and it has quite a bit on one or two towers.

[TPIGroove]

Good news, there's a crusty indoor salvage yard in St. Louis that had rows upon rows of parts to cannibalize. A 550F (?, has 022A stamped on it) carb set was incomplete, so I could take the individual body off. Casting is a 99% match, only difference I saw is the top cover's screw hole isn't drilled all the way through. Did a quick cleanup and it's in very good shape overall, just has a minor cosmetic scuff on the outside.

[TwoTired]

The numbers on the carb bodies refer to what parts are installed in the bodies and the settings the factory used to match the metering required by exhaust and intake sold with the bike.

069A was the F model set up for all years of the CB550.

022a was used on the Cb550 K0 and K1.  There may have been a transition to 087a for the K2 Cb550.  Not sure what parts are different though.  Maybe the pilot screws.

To reiterate, the bodies are the same (apart from the stamping).  Transfer parts from an 069A to a body stamped 022A and it should function like a 069a stamped carb.  ...And confuse the heck out of the next guy to work on the carbs, which now won't have the expected parts inside.

Cheers,

[dave500]

just on a side note im not sure if also those air bleeds in the bodies changed Loyd?

[TwoTired]

just on a side note im not sure if also those air bleeds in the bodies changed Loyd?

Hi Dave!

In my encounters:
The 022a came with hollow tipped pilot screws. US K models 1974 through 1975.
The 069a came with solid tipped pilot screws. US  F models 1975 through 1977.
The 087a found on 1976 K2 carbs I acquired had all the same internal parts and settings as the 022a, except it had solid tipped pilot screws.  I could find no other differences the carb bodies among all the samples I have.

I must mention that although I was told the 087a carb bank I acquired was original from a member here, it came separate from a bike, and I was unable to verify it unconditionally as unmolested.  But, it makes some logical sense on the timeline march toward EPA acceptance criteria taking effect in 1978.

I have a spec sheet that specifies the pilot screw tip taper changed from the 022a to the 069a (hollow to solid tipped).  I am unable to verify if the body’s seats were correspondent.  If so, the bodies would indeed be technically different, too.  But, I wouldn’t  expect any noticeable change in functionality, apart from standard pilot screw setting among them.

Lastly, the Honda shop booklet I have shows the same carb settings for all CB 550 models for K0,K1, and K2, and different settings for the F models.

For completeness, there is also a 649 stamped Keihin carb body, which is reportedly found in Europe and perhaps Canada, whose settings and specs. are unknown to me, and samples of which I have never seen.  These were paired with a different air filter  top with a smaller inlet than those found in all US models.  I’ve only seen pictures of this, and have no first hand experience.  All info I have about these carbs came from this forum.  I suspect there must be some other change, perhaps in the carb body, to correspond with the smaller air inlet.  But, I have no credible source to confirm that hypothesis, only extrapolation about how these carbs must obey physical laws.

Cheers!

[dave500]

in the mouth of the carbs the bleeds that serve the emulsion tube and idle circuit,they have a pressed in brass insert,i think these are different?ive never found any solid info on them,orifice diameter etc?

[PeWe]

Is it the 10% ethanol fuel that  corrode like that?

My K6 was parked 1990 with unleaded ethanol free fuel.
Carbs cleaned 2017. It was a red slimy goo inside float bowls. Almost no corrosion at all inside. Man jet holders and bowl alu not corroded at all.

[ekpent]

 Most of time I see that it was from water. Somebody probably already cleaned those carbs previously because the bowls would have been loaded up with a lot of white powder. Whether the water was drawn in by ethanol or another source could be debatable.

[TwoTired]

Ethanol absorbs water to a point.  But, it also reacts with water forming aldehydes and acids.

In a flowing system, it's all burned in the combustion chamber and replaced with un-reacted replacements.

Sitting in a bowl the acids start reacting and dissolving metal bits.  Time is the enemy.  The longer it sits, the more damage.

Water forms in the carb bowls due to condensation.  The bowls are vented to atmosphere where humidity exists.  Daily temperature swings create expansion and contraction of the air, which allows the carbs to "breathe in" more moisture from the air. It then condenses on internal walls of the chamber during a temperature fall when the aair can't hold the moisture, like dew, to mix with fuel and or corrode the insides of the float bowl chamber.

Most machines don't like to sit without work.  Ethanol fuel makes the acceptable sitting duration shorter before damage occurs.

Cheers,

[TwoTired]

in the mouth of the carbs the bleeds that serve the emulsion tube and idle circuit,they have a pressed in brass insert,i think these are different?ive never found any solid info on them,orifice diameter etc?

Yes.  Those are #150 jets in the ones I measured (627b, 022a, and 069a).  I'll have to find the 087a set I have to measure those.  Still stored in the move boxes.

Cheers,

[Deltarider]

I wonder if TT is sure his set of 087A carbs have the solid tip airscrews. When asked, no owners of 87A carbs have reported the solid tip airscrews inside. So far they all reported the hollow and cross drilled airscrews. The reason I wonder, is because of what TT wrote previously (June 7^th, 2011):

There was a post that said the air bleed screws were solid tipped rather hollow and cross drilled, referencing a Honda parts list.  Would you check yours?  I can't be certain if my set was "meddled", as it has the hollow screws, and there are other signs they aren't "virgin".

There's a possibility TT has more than one set of 87A carbs ofcourse, but - again - nobody so far has found the solid tip airscrews in their 087a carbs. This in spite of what the American (!) Honda Parts list describes on p.C10 (part #7).http://www.honda4fun.com/pdf_parts_list/pdf_spac550/CB550-K0-K1-K2/CB550-K0-K1-K2_04.pdf
For the sake of gathering as much reliable info as possible, owners of a CB550K2, the only model that had the 087A carbs, are kindly requested to report what airscrews they have in theirs. Tip: do not unscrew airscrews before you have established what position they are in. You can do this by first turning them all the way in (gently) and count. Make a note of it and you can screw them in again in the position they were.
My overview of the oldstyle CB500/550 carbs below is - as always - open for falsification so all findings are welcome.

[goodtryer]

So, I spoke to a metallurgist in our office and showed him the pictures from the top of this post. He said there is a serious problem with aluminum corrosion in floating-roof tanks where products containing ethanol are stored. He said the problem has accelerated with the advent of "dry ethanol" which has water content below 0.1 vol%. Apparently, the higher water content helped/enabled/allowed/preserved (I'm not sure of the exact word technically, but you get the point) a protective layer on the aluminum. The dry ethanol, in contrast, does not and leads to "dry corrosion." ("the oxide layer of the aluminum is damaged.. and cannot repassivate in water-free media..")

First, the discussion about high water content leading to corrosion is correct. However, the distinction is that the water content that leads to the acid formation and corrosion is very high, "9.5% (at 20 deg C). Thus, it is beyond the statutory fuel compositions of most countries (e.g. DIN EN51625 and ASTM D5798-10)." Essentially, fuel with this much water in it is "bad" or "spoiled" and we all know bad gas is to be avoided or bad outcomes can be expected.

"Dry ethanol" is a different problem. The fuel itself, when delivered within spec, will cause "dry corrosion" in aluminum and magnesium alloys. Importantly, the effect is accelerated with increased temperature.

Attached is a PDF file detailing an experiment on this exact topic, found on the web here:
https://www.process-design-center.com/shared/hydrous-ethanol/Corrosion,%20Polymers%20&%20Elastomers/IAV%20-%20Article%20Corrosion%20behaviour%20of%20Aluminium%20Alloys%20in%20Ethanol%20Fuels.pdf

A couple of relevant quotes from the PDF:

Since 2008, for mixed fuels in Europe a water content below 0.3 vol.% is required (DIN EN 51625). This value must be guaranteed at the petrol pump. Since the water content of alcohol increases during the storage, because of the hygroscopic effect of ethanol and the improved synthesizing process, there are fuels offered with water content below 0.05 vol.% now. This can lead to dry corrosion.

Besides the temperature, the water content was detected to be the biggest catalyst of ethanol induced corrosion. The corrosion attack was indicated by intensive gas formation at the surface of the specimens, followed by the growth of a deck layer on the surface and a turbidity of the medium. It was observed that the corrosion process occurs in two phases. In the first phase, local corrosion was formed at the places from which gas bubbles floated up and the reaction products were formed. In the second phase of the reaction, the corrosion mechanism changed to a uniform attack. The corrosion products formed a porous, relatively consistent growing layer on the surface.

The experiments have shown that under the present conditions dry corrosion strongly depends on temperature and water content, whereas the content of ethanol and the grain size of the aluminium are of secondary importance. To trigger dry corrosion, the water content must fall below a critical level. In these tests this level was near to 0.2 vol.% water in the ethanol–fuel mixture. From this experimental work it is not certain if these values are temperature dependent. Furthermore, immersion experiments demonstrated that temperatures close to the boiling point of ethanol induce strong corrosion attack. However, even at 60 C and after an exposure time of 336 h corrosion was found. This suggests that the dry corrosion occurs at this temperature (with reduced reaction rate). The variation of the ethanol content of the solutions shows, that the dry corrosion also depends on this value. The incubation, which is the time until the corrosion attack starts, decreases and the number of pits rises with increasing ethanol content. However, the corrosion attacks in all investigated cases were so extensive that a component failure would occur.
The results of electrochemical tests and the immersion tests of aluminium alloys with noble precipitates (aluminium–copper alloys) suggest that dry corrosion is a predominantly chemical mechanism.

Hope this helps. I know I'll be searching for a source for ethanol-free gas around here.

Cheers