why does my street, sport, motorcycle automatically (without my input) lean into a strong wind gust?

You are leaning into the gust....its instinctual. If you didnt lean into it....you would wipe out. Your subconcious has a self preservation reflex that makes lean without really noticing it. No matter what the explanation...the Motorcycle is not leaning on its own. Its just a machine doing what its told.

You and your bike lean into the wind because it's acting like a sail. The wind gets caught up below the center of gravity where the weight distribution is the least from a cross-wind perspective (down by the wheels) which in-turn pushes the wheels away from the wind, or gives the feeling of leaning into the wind. It happens often when you pass a tractor-trailer on the highway. You will feel it as you get by the nose of the truck. The feeling is worse on lighter bikes than heavier bikes..

Full fairing have a tendendance to act as a wing and apply lift to the front end of the bike so when you are hit by the cross wind the shearing action created will give you a slight lean in effect as the lower portion of the bike is pushed by the wind in the direction it is blowing.

I don't know about these other answers but the instinct thing is it most of the time. Although if the crosswind is substantial enough it pushes on the front tire. That push can move the front wheel enough to experience a slight counter steer. If you push on the handlebar (at speeds high enough) the bike will lean to the side you are pushing (counter-steer). A high wind can push on the nose of the tire enough to put the bike in a lean. It takes very little force on the handle bars to counter-steer. The wind has to blow a little harder or be suddenly introduced into the situation to effect your course.

There's an equal amount of pressure on every object. When you remove the pressure from one side of an object, it will tend to move or vice-versa... like when you drive by a garbage can really fast, it moves into the car b/c you removed the pressure from one side of the can and there was more pressure on one side than the other. Therefore, the wind could either act in two ways: pushing you with the force of the wind in one direction or the aerodynamics of you on your bike can disperse the pressure around you and the opposite pressure would push you toward the wind. Hope this answers your question.

I know the feeling. I ride a 125cc that weights 120kg and I weight 75kg, 195kg combined! When a gust occurs, the bike shifts to the side, which makes me **** myself if a car is in the other lane. What I do is simply slow down, going faster makes things much worse. Avoid bridges, and if you do go over one, Slow as possible!! Try to take a route that's not open, like lots of houses around or trees. Basically, unless your riding a heavy bike, like a Chopper or a Tourer, avoid windy days all together. The cold, heat and rain I can brave, but the wind will get you killed!

Actually, Your body acts as a sail, and as you experience those wind gust they push you and you bike the same way a sail would push a boat across the water. But given forward momentum and the fact that your tires are indeed gripping the road you get the same effect as if a friend lightly pushes you to try and squeeze by in the hallway.

You ride in the wind "without my hands on the handlebars"?!!?

Well, young Thomas Edison, the answers above are all correct - you are unconsciously leaning into the wind, or your Ninja is haunted by the ghost of the last idiot who rode around with his hands off the bars.

I drive a Suzuki Volusia 800 touring bike. The bike does not lean by itself but you do it without realizing it with your lower body to compensate for the movement of the bike.

Gyroscopic effect.

A motorcycle in motion is a big spinning gyroscope, and when you apply a force to a spinning gyroscope it pushes back. Try it with a spinning top - same thing happens.

The phenomena is called 'rigidity in space'

:-)