I've used this old school trick on many gasoline engines over the years. I take a spray bottle full of water and spray it into the intake of a running engine while revving it up. You might think that the water would put out the fire but it doesn't. It creates steam inside the combustion chamber and cleans the valves, head, top of the piston, spark plugs, everything.
I am a bit leery of doing this to my EFI 96", however.
It had been running rich and fowling plugs so I think it could use a good cleaning, but I don't know if it would be bad for the O2 sensors.
Has anyone had any experience using this technique on a fuel injected V-twin?

 

I would not do it unless there was a real problem from someone using too much stabilizer or octane boots and carboned it up to the point that it raised compression to the point it had a spark knock. That carbon is sharp and will scratch cylinder and a lot will get caught in that small gap on top of the first ring between the piston and cylinder. Doing it also put tremendous pressure on the crank and rod bearings and those are roller on the big bearing end in your engines. Could easily put groove lines in crank pin.

Back when we had leaded gas, carbon would continue to build up.

With unleaded, it only gets so thick and crumbles off in small flakes that blow out.

There is a few posting of it on the piston top on here that is very misleading do to the fact that it is from an engine that either has poor oil control and owner used additives.

There is also a lot of liquid oil that has ran on top and that is from the drain hole in the side return port spilling out and running on the piston.

It will blast it off however but like mentioned above is extremely dangerous and rough on an engine. My aluminum head Z had a leak and I kept ignoring it till it broke starter bell and I tore it down. That first attachment is how the piston looked from the small water leak between the head and block when I popped the head. Engine has 100k on it. The leak got worst when motor cooled off and leaked into cylinder. It locked on starting and broke the starter motor off.

You can also see how unleaded gas buildup actually flakes off.

 

Modern engines are no longer old school! We may like to think that little has changed with our Harleys over the decades, but under the skin they are very different animals today. I wouldn't spray water into any of my engines. Get that wrong and it will need major surgery pdq!

 

That is one clean piston!

 

^^ They will get clean if the head gasket is leaking anti freeze into that cylinder. that is similar to the water trick.

 

^^^^What he said.

Spritzing a wee bit of water into your intake for a minute or two will NOT make your piston look like that.

 

Just ride in the rain.

 

I have done it on my 2008 FLHTC. Didn't hurt a thing. Don't think it improved anything either.

 

If I was going to spray anything into the intake it would be Seafoam, not water. But even before that I would put in a new set of stock plugs and ride it at high rpm's for a nice long time. Not saying redline it or bang the rev limiter, but keep it in the 4-5000 range. With a healthy motor it won't hurt to do that. Might even help.

 

Yep. Seeing how a blown head gasket can clean a cylinder is probably how people came up with the water trick.