® The water tune

The water tune. It's controversy rests in the fact that most people envision something very different than what I am going to describe here -- something slimy and underhanded -- when they think of this procedure. You know, something 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 of that. That's not what this is. Done correctly, water treatment of an engine's combustion chambers is an entirely legitimate operation, though no substitute for an actual valve job. 2

First, why? Why do this? Do this only if cylinder compression is low, or ond of more cylinders read appreciably different compression than the rest, 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 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 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 also to ride the bike a bit after 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. 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 Said several times already. 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.

Last updated November 2021
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