Hi,

My GS500 lets out a puff of blue smoke at highway (100km/h) speeds when I close the throttle.

What would be causing a new bike to burn oil like that?

Bike was purchased from new and has 1800kms on it, had first service at 980kms.

Many thanks.

Leaky valve stems possibly.. the motor is trying to pull in air with the throttles closed, it is easier to pull air (or oil) from the valve stem seals if they are leaking.

gasket

Diesel in fuel 

seriously my friend got some(litlle) diesel by accident into tank, so his bike would smoke every time he changed gear.