Carbon

[mikenixon]

Had a good Gold Wing customer. He complained of an odd noise on deceleration. Sure enough, wringing the rpm up then snapping the throttle shut would, as the rpm fell below 3,000, produce a loud tapping noise before the engine quieted again at idle. So I took a cylinder head off. Couldn't see anything wrong. Then, looking down, whoa! There it was. Marks on the piston crown where it was gently closing the sticking exhaust valve.

Seems the customer had been using only premium gas and as a consequence the exhaust valves carboned up so bad they were beginning to stick in their guides, as confirmed by the appearance of the valves when later removed.

Hard to believe? This scenario actually repeated itself almost 40 years later. This time it was a Kawasaki ZX-6R that was missing at high rpm. A handful of mechanics had examined it and couldn't come up with a cause even after replacing the ECU and eventually disassembling and inspecting the engine. The hero that day also took the cylinder head off and got a look at the valves, and noticed something the others missed -- excessive carbon buildup on the exhaust valves.

What was happening, it was proved by oscilliscope measurement, was the ZX-6's ECU, programmed to not allow the engine to pollute, was detecting the miniscule change in dynamic cylinder pressure resulting from the carboned-up exhaust valves' slowed closing, and was turning off the ignition coils to prevent HC emissions increase, creating the loss of two cylinders at high speed. Cleaning the valves solved the misfire. True story, and I often related this episode to my Kawasaki dealer students when explaining that vehicle ECUs contain things we really don't know much about.

[desertrefugee]

Too bad for sure is with an actual physical inspection after pulled ahead. Are there steps that could be taken to address carbon build-up on a motorcycle without disassembly? I vaguely recall an old shade tree trick for Automotive engines of slowly introducing water into the intake while it's running. I fully understand this practice is fraught with Peril, and should never be done on a Goldwing or any other motorcycle engine, but are there other methods that might be employed that could reduce carbon build-up?

[desertrefugee]

Sorry about the fractured in English. Voice recognition not working well on the tablet today. Should have read "Too bad diagnosis is only possible with disassembly".

[mikenixon]

Hi, Darrell! Actually, the water thing is a legitimate technique. But it isn't done the way people think. And yes, hydrolock is a possibility if done incorrectly.

[rcmatt007]

I often see the "I run premium" debate.... these engines were not made for higher octane. So besides wasting money, you have given us another reason why not to.

[flyday58]

And thanks again personally for octane advice you gave me a little while back. While we didn't discuss specifics, your explanation then of what octane ratings are all about has stayed with me, and I try to pass it on when I can. Kudos on another informative thread.

[mikenixon]

[mikenixon]

Darrell asked about this, otherwise I would probably not get into it. The controversy surrounding water treatment of a combustion chamber centers around the fact that most people envision something very different than the thing we'll explore here -- something slimy and underhanded -- when they think of this procedure. You know, a thing done late at night in a shed behind the used car lot, by the same guy that puts banana peels in the transmission and sawdust in the differential. Shudder. 1

Forget all that. That's not what this is. Done correctly, water treatment of an engine's combustion chambers is entirely legitimate, though no substitute for an actual valve job. 2

First, why? Why do this? Do this only if cylinder compression is low, or if the engine idle is unstable, or you experience dramatic changes in valve clearances. While there are other reasons for these glitches unrelated to carbon, carbon is a common, frequent factor. Japanese engines in particular don't like a lot of carbon buildup and often respond by their valves beginning to leak (or in extreme cases stick) and thus this is a common source of lost cylinder compression and the other issues. 3 Water treatment can restore compression lost to heavy carbon accumulation around the valve sealing surfaces (faces). It will however do no more than this. It won't compensate for worn valves or valve seats. Keep this in mind. 4

Here is the correct technique. Get a glue bottle, cleaned of glue or anything else inside. It needs to be transparent or at least translucent. Add to this a 6-inch length of clear hose that will fit tightly on the end of the bottle. I use old battery vent hose. You also need at least one carburetor syncing vacuum adapter (probe), and make sure the hose you are using fits snugly on this probe. Lastly, I like to use distilled water but I doubt it will make a difference if you use tap water.

Warm the engine to operating temp. Shut it off and install your sync probe. Fill the glue bottle 2/3 full with water. Make sure the hose fits snugly on its top. Attach bottle and hose to the sync probe and fold the hose completely in half to prevent water entering the engine when it is started -- this is important. Uncontrolled entry of water into the engine can result in cylinder hydrolock that can bend a connecting rod. 5

Restart the engine. The hose is still bent in half. Raise engine rpm to a minimum of 3,000 rpm and carefully unkink the hose to the point that dribbles of water are sucked into the intake manifold. Keep the rpm up, and carefully limit water intake. 6 You want dribs and drabs, not a stream. Slowly. Watch the water level in the glue bottle. After a quarter to half inch of the water has gone into the cylinder, pinch the hose shut again and raise the engine rpm with a few revs to dry out the cylinder. Shut the engine off, move your sync probe to another cylinder (remembering to replace the previous cylinder's vacuum screw) and repeat. I like to ride the bike a bit after all cylinders are treated to ensure no water vapor is left in the cylinders.

What does this do? What happens is the water hits the combustion chamber and instantly turns to steam, very effectively knocking loose the carbon that is adhering to the piston crown and valves. It's a classic procedure. I helped a student do this on his Harley-Davidson Sportster one time and carbon visibly flew out the exhaust and speckled an onlooker's trousers. It really works.

Many have asked why simply spraying water into the carburetor entrance using a plant sprayer wouldn't work as well. It won't. Water intaked this way is already atomized, too finely atomized to provide the shock we want the combustion chamber to receive. 7

So you see, this isn't shade-tree. But neither is it a cure-all. It's basically a "let's try this before we pull the head off" thing. Or, a "man, there's a lot of carbon in there" thing. And it can be very effective, even though it can't replace a proper valve job. Recheck your valve clearances after the water treatment because when significant carbon is removed, clearances will likely change. A final compression test is a good idea also.

1 The water treatment has in many minds a certain stigma. Done correctly and for the right reason, it doesn't deserve that.

2 If you have paid attention in recent months you know how much a stickler I am for best practice methodology in regard to valve jobs.

3 Certain things cause higher than normal carbon buildup. Fuel meant for older vehicles, fuel additives, incorrect air/fuel mixtures (including overuse of the choke), and oil consumption are some of them.

4 This article will say this several times. A valve job (I do ten or twelve every year) is always the very best way to optimize cylinder compression and therefore engine performance. Consider the water treatment merely a way to reverse bad engine maintenance inflicted by a previous owner.

5 Careful. Hydrolock is serious.

6 The engine rpm is kept up because you want to elevate engine heat somewhat to maximize the steam conversion, and because the engine would have an unstable idle during the procedure anyway.

7 I realize many will claim there is no difference, but there really is.

[mikenixon]

Yamaha sells a product called Ring Free that is fairly well known among four-stroke outboard motor users, though I have never heard of anyone in powersports using it. It's a fuel additive and like other additives can be questionable in its effect. I know very little else about it so others feel free to comment. But the water treatment is a well-established procedure and one I am pretty familiar with.

[rcmatt007]

A few years back we really cleaned out the carbon on the right side of our 1200.... unfortunately it was a blown head gasket... but dang, the cylinders, valves and heads were clean!

[mikenixon]

A few years back we really cleaned out the carbon on the right side of our 1200.... unfortunately it was a blown head gasket... but dang, the cylinders, valves and heads were clean!

LOL!

[DUGG]

Seems the customer had been using only premium gas and as a consequence the exhaust valves carboned up so bad they were beginning to stick in their guides. excessive carbon buildup on the exhaust valves.

Can you explain why this was caused by premium grade. It would seem the additive package in brand X gas would be the same regardless of grade of fuel.

[mikenixon]

Hi, DUGG. Sure.

"Premium" grade pump gasoline is more than just the one with the highest octane. Traditionally, it is been formulated to suit older engines thus contains more detergents and lubricants. These concessions to cast iron V8s behave well in their target engines, but not so much in modern engines where they are not only unnecessary but get left behind as excessive carbon deposits. Carbon buildup leading to valve malfunction and valve sealing loss result. Many over the counter fuel additives do this also in Hondas.

[rcmatt007]

I would think it is also that it burns slower

[Solina Dave]

Hi Mike,

I have a '78 GL, since new, with many miles. For the past couple of years I've been quite diligent in filling up with premium fuel. I've been doing so as a way to avoid fuel with ethanol content, which is supposedly harmful to early GL engine components. A lot of this thread is way over my head, but It seems like a trade-off is apparent. Could you comment on that for me?

Thanks............ ...Dave