Why does my bike...
 

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Have you tried turning it off, then turning it back on? :lol

First things I'd check:
- cupped/squared-off tires (particularly the front); can look fine at first glance, but cupping/feathering in particular can cause some very jacked-up handling
- steering head bearings; lift front w/ stem stand, feel for notchy or loose action when pivoting & pull wheel front-to-back, feeling for looseness
- wheel bearings; spinning freely?
- rear wheel alignment; adjusted chain or replaced tire recently? I think it would have to be off pretty badly to feel as you described, but it's worth a check

http://www.motorcyclistonline.com/ho...els/index.html

Also check out some of these troubleshooting ideas.
http://www.sportrider.com/tech/146_0...ble/index.html

It might be time for refreshing the suspension.
Get some springs set for your weight, and redo your front forks.

has your bike been crashed recently? if so, check all your suspension components, particularly the forks for bends/damage, along with the wheels themselves for bending.

how old are your tires? has it been lowered any? if it has, you may have to adjust the front forks a little to square them up in the triples.

Sounds like steering head bearings, assuming your tires are ok.

You might also be low on blinker fluid.

JC

Turn the bars back and forth and see if you feel a "notch" in the middle.

Sounds like bearings.

Your steering bearing can mess with how your ride feels. And since it is gradual, you don't really notice it.

Mine were clunking, I had em changed and the bike felt like I'd spent 2000 dollars freshening up the suspension, and I barely noticed since it was gradual. I just thought I wasn't feeling comfortable on the bike.

When my steering head bearings got loose it felt like a warped rotor when I'd hit the brakes hard.

I had something similar happen on my first bike. It was the steering head bearings.