If its like the 750, the headlight ears are masking the sin. If it has that design. The tubes under the headlight ears are corroded and not allowing the tubes to slide up into the upper clamps.
Be careful with all the clamps loosened and pushing down on the front end. If it decided to move, the tubes could come up thru the clamps fast and hard and you'll end up on the ground. Depending on the design, they could hit and stop at the handlebars. Just be careful.
AS stated, remove the front wheel, block up the front end, and twist and turn each tube individually with some lube. If its of the design to allow it, pry open the upper and/or lower clamp just a tad.